NEW HAMPSHIRE v. MAINE on motion to dismiss complaint

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742 OCTOBER TERM, 2000
Syllabus
NEW HAMPSHIRE v. MAINE
on motion to dismiss complaint
No. 130, Orig. Argued April 16, 2001—Decided May 29, 2001
New Hampshire and Maine share a border that runs from northwest to
southeast. At the border’s southeastern end, New Hampshire’s east-
ernmost point meets Maine’s southernmost point. The boundary in
this region follows the Piscataqua River eastward into Portsmouth
Harbor and, from there, extends in a southeasterly direction into the
sea. In 1977, in a dispute between the two States over lobster fish-
ing rights, this Court entered a consent judgment setting the precise
location of the States’ “lateral marine boundary,” i. e., the boundary in
the marine waters off the coast, from the closing line of Portsmouth
Harbor five miles seaward. New Hampshire v. Maine, 426 U. S. 363;
New Hampshire v. Maine, 434 U. S. 1, 2. The Piscataqua River bound-
ary was fixed by a 1740 decree of King George II at the “Middle of the
River.” See 426 U. S., at 366–367. In the course of litigation, the two
States proposed a consent decree in which they agreed, inter alia,
that the descriptive words “Middle of the River” in the 1740 decree
refer to the middle of the Piscataqua River’s main navigable channel.
Rejecting the Special Master’s view that the quoted words mean the
geographic middle of the river, this Court accepted the States’ inter-
pretation and directed entry of the consent decree. Id., at 369–370.
The final decree, entered in 1977, defined “Middle of the River” as
“the middle of the main channel of navigation of the Piscataqua River.”
434 U. S., at 2. The 1977 consent judgment fixed only the lateral marine
boundary and not the inland Piscataqua River boundary. In 2000, New
Hampshire brought this original action against Maine, claiming on the
basis of historical records that the inland river boundary runs along
the Maine shore and that the entire Piscataqua River and all of Ports-
mouth Harbor belong to New Hampshire. Maine has filed a motion
to dismiss, urging that the earlier proceedings bar New Hampshire’s
complaint.
Held: Judicial estoppel bars New Hampshire from asserting that the
Piscataqua River boundary runs along the Maine shore. Pp. 749–756.
(a) Judicial estoppel is a doctrine distinct from the res judicata doc-
trines of claim and issue preclusion. Under the judicial estoppel doc-
trine, where a party assumes a certain position in a legal proceeding,
and succeeds in maintaining that position, he may not thereafter, simply
because his interests have changed, assume a contrary position, espe-

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cially if it be to the prejudice of the party who has acquiesced in the
position formerly taken by him. Davis v. Wakelee, 156 U. S. 680, 689.
The purpose of the doctrine is to protect the integrity of the judicial
process by prohibiting parties from deliberately changing positions
according to the exigencies of the moment. Courts have recognized
that the circumstances under which judicial estoppel may appropriately
be invoked are not reducible to any general formulation. Nevertheless,
several factors typically inform the decision whether to apply the doc-
trine in a particular case: First, a party’s later position must be clearly
inconsistent with its earlier position. Second, courts regularly inquire
whether the party has succeeded in persuading a court to accept that
party’s earlier position, so that judicial acceptance of an inconsistent
position in a later proceeding would create the perception that either
the first or the second court was misled. Third, courts ask whether the
party seeking to assert an inconsistent position would derive an unfair
advantage or impose an unfair detriment on the opposing party if not
estopped. In enumerating these factors, this Court does not establish
inflexible prerequisites or an exhaustive formula for determining the
applicability of judicial estoppel. Additional considerations may inform
the doctrine’s application in specific factual contexts. Pp. 749–751.
(b) Considerations of equity persuade the Court that application of
judicial estoppel is appropriate in this case. New Hampshire’s claim
that the Piscataqua River boundary runs along the Maine shore is
clearly inconsistent with its interpretation of the words “Middle of
the River” during the 1970’s litigation to mean either the middle of the
main navigable channel or the geographic middle of the river. Either
construction located the “Middle of the River” somewhere other than
the Maine shore of the Piscataqua River. Moreover, the record of the
1970’s dispute makes clear that this Court accepted New Hampshire’s
agreement with Maine that “Middle of the River” means middle of
the main navigable channel, and that New Hampshire benefited from
that interpretation. Notably, in their joint motion for entry of the con-
sent decree, New Hampshire and Maine represented to this Court that
the proposed judgment was “in the best interest of each State.” Were
the Court to accept New Hampshire’s latest view, the risk of incon-
sistent court determinations would become a reality. The Court cannot
interpret “Middle of the River” in the 1740 decree to mean two different
things along the same boundary line without undermining the integrity
of the judicial process. Pp. 751–752.
(c) The Court rejects various arguments made by New Hampshire.
The State urged at oral argument that the 1977 consent decree simply
fixed the “Middle of the River” at an arbitrary location based on the
parties’ administrative convenience. But that view is foreclosed by

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Syllabus
the Court’s determination that the consent decree proposed a wholly
permissible final resolution of the controversy both as to facts and law,
426 U. S., at 368–369. The Court rejected the dissenters’ view that
the decree interpreted the middle-of-the-river language “by agreements
of convenience” and not “in accordance with legal principles,” id., at 369.
New Hampshire’s contention that the 1977 consent decree was entered
without a searching historical inquiry into what “Middle of the River”
meant is refuted by the pleadings in the lateral marine boundary case
and by this Court’s independent determination that nothing sug-
gests the location of the 1740 boundary agreed upon by the States is
wholly contrary to relevant evidence, ibid. Nor can it be said that
New Hampshire lacked the opportunity or incentive to locate the river
boundary at Maine’s shore. In its present complaint, New Hampshire
relies on historical materials that were no less available in the 1970’s
than they are today. And New Hampshire had every reason to consult
those materials: A river boundary running along Maine’s shore would
have resulted in a substantial amount of additional territory for New
Hampshire. Pp. 752–755.
(d) Also unavailing is New Hampshire’s reliance on this Court’s rec-
ognition that the doctrine of estoppel or that part of it which pre-
cludes inconsistent positions in judicial proceedings is ordinarily not
applied to States, Illinois ex rel. Gordon v. Campbell, 329 U. S. 362, 369.
This is not a case where estoppel would compromise a governmental
interest in enforcing the law. Cf. Heckler v. Community Health Serv-
ices of Crawford Cty., Inc., 467 U. S. 51, 60. Nor is this a case where
the shift in the government’s position results from a change in public
policy, cf. Commissioner v. Sunnen, 333 U. S. 591, 601, or a change in
facts essential to the prior judgment, cf. Montana v. United States, 440
U. S. 147, 159. Instead, it is a case between two States, in which
each owes the other a full measure of respect. The Court is unable
to discern any substantial public policy interest allowing New Hamp-
shire to construe “Middle of the River” differently today than it did
25 years ago. Pp. 755–756.
Motion to dismiss complaint granted.
Ginsburg, J., delivered the opinion of the Court, in which all other
Members joined, except Souter, J., who took no part in the consideration
or decision of the case.
Paul D. Stern, Deputy Attorney General of Maine, argued
the cause for defendant. With him on the briefs were An-

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drew Ketterer, Attorney General, and Christopher C. Taub
and William R. Stokes, Assistant Attorneys General.
Jeffrey P. Minear argued the cause for the United States
as amicus curiae. With him on the brief were former Solic-
itor General Waxman, Assistant Attorney General Schiffer,
Deputy Solicitor General Kneedler, and Patricia Weiss.
Leslie J. Ludtke, Associate Attorney General of New
Hampshire, argued the cause for plaintiff. With her on the
briefs were Phillip T. McLaughlin, Attorney General, and
John R. Harrington.
Justice Ginsburg delivered the opinion of the Court.
The Piscataqua River lies at the southeastern end of
New Hampshire’s boundary with Maine. The river begins
at the headwaters of Salmon Falls and runs seaward into
Portsmouth Harbor (also known as Piscataqua Harbor). On
March 6, 2000, New Hampshire brought this original action
against Maine, claiming that the Piscataqua River bound-
ary runs along the Maine shore and that the entire river
and all of Portsmouth Harbor belong to New Hampshire.
Maine has filed a motion to dismiss on the ground that
two prior proceedings—a 1740 boundary determination by
King George II and a 1977 consent judgment entered by this
Court—definitively fixed the Piscataqua River boundary at
the middle of the river’s main channel of navigation.
The 1740 decree located the Piscataqua River boundary
at the “Middle of the River.” Because New Hampshire, in
the 1977 proceeding, agreed without reservation that the
words “Middle of the River” mean the middle of the Pis-
cataqua River’s main channel of navigation, we conclude
that New Hampshire is estopped from asserting now that
the boundary runs along the Maine shore. Accordingly, we
grant Maine’s motion to dismiss the complaint.
I
New Hampshire and Maine share a border that runs from
northwest to southeast. At the southeastern end of the

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border, the easternmost point of New Hampshire meets the
southernmost point of Maine. The boundary in this region
follows the Piscataqua River eastward into Portsmouth
Harbor and, from there, extends in a southeasterly direction
into the sea. Twenty-five years ago, in a dispute between
the two States over lobster fishing rights, this Court entered
a consent judgment fixing the precise location of the “lateral
marine boundary,” i. e., the boundary in the marine waters
off the coast of New Hampshire and Maine, from the closing
line of Portsmouth Harbor five miles seaward to Gosport
Harbor in the Isles of Shoals. New Hampshire v. Maine,
426 U. S. 363 (1976); New Hampshire v. Maine, 434 U. S. 1, 2
(1977). This case concerns the location of the Maine-New
Hampshire boundary along the inland stretch of the Pis-
cataqua River, from the mouth of Portsmouth Harbor west-
ward to the river’s headwaters at Salmon Falls. (A map of
the region appears as an appendix to this opinion.)
In the 1970’s contest over the lateral marine boundary,
we summarized the history of the interstate boundary in the
Piscataqua River region. See New Hampshire v. Maine,
426 U. S., at 366–367. The boundary, we said, “was in fact
fixed in 1740 by decree of King George II of England” as
follows:
“ ‘That the Dividing Line shall pass up thro the Mouth
of Piscataqua Harbour and up the Middle of the
River . . . . And that the Dividing Line shall part
the Isles of Shoals and run thro the Middle of the Har-
bour between the Islands to the Sea on the Southerly
Side. . . .’ ” Id., at 366 (quoting the 1740 decree).
In 1976, New Hampshire and Maine “expressly agree[d]
. . . that the decree of 1740 fixed the boundary in the Pis-
cataqua Harbor area.” Id., at 367 (internal quotation marks
omitted). “Their quarrel was over the location . . . of the
‘Mouth of Piscataqua River,’ ‘Middle of the River,’ and ‘Mid-
dle of the Harbour’ within the contemplation of the decree.”

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Ibid. The meaning of those terms was essential to delineat-
ing the lateral marine boundary. See Report of Special
Master, O. T. 1975, No. 64 Orig., pp. 32–49 (hereinafter Re-
port). In particular, the northern end of the lateral marine
boundary required a determination of the point where the
line marking the “Middle of the [Piscataqua] River” crosses
the closing line of Piscataqua Harbor. Id., at 43.
In the course of litigation, New Hampshire and Maine
proposed a consent decree in which they agreed, inter alia,
that the words “Middle of the River” in the 1740 decree refer
to the middle of the Piscataqua River’s main channel of navi-
gation. Motion for Entry of Judgment By Consent of Plain-
tiff and Defendant in New Hampshire v. Maine, O. T. 1973,
No. 64 Orig., p. 2 (hereinafter Motion for Consent Judgment).
The Special Master, upon reviewing pertinent history, re-
jected the States’ interpretation and concluded that “the
geographic middle of the river and not its main or naviga-
ble channel was intended by the 1740 decree.” Report 41.
This Court determined, however, that the States’ inter-
pretation “reasonably invest[ed] imprecise terms” with a
definition not “wholly contrary to relevant evidence.” New
Hampshire v. Maine, 426 U. S., at 369. On that basis, the
Court declined to adopt the Special Master’s construction
of “Middle of the River” and directed entry of the consent
decree. Id., at 369–370. The final decree, entered in 1977,
defined “Middle of the River” as “the middle of the main
channel of navigation of the Piscataqua River.” New Hamp-
shire v. Maine, 434 U. S., at 2.
The 1977 consent judgment fixed only the lateral marine
boundary and not the inland Piscataqua River boundary.
See Report 42–43 (“For the purposes of the present dis-
pute, . . . it is unnecessary to lay out fully the course of the
boundary as it proceeds upriver . . . .”). In the instant ac-
tion, New Hampshire contends that the inland river bound-
ary “run[s] along the low water mark on the Maine shore,”
Complaint 49, and asserts sovereignty over the entire river

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and all of Portsmouth Harbor, including the Portsmouth
Naval Shipyard on Seavey Island located within the harbor
just south of Kittery, Maine, id., at 34.* Relying on various
historical records, New Hampshire urges that “Middle of the
River,” as those words were used in 1740, denotes the main
branch of the river, not a midchannel boundary, Brief in
Opposition to Motion to Dismiss 12–16, and that New Hamp-
shire, not Maine, exercised sole jurisdiction over shipping
and military activities in Portsmouth Harbor during the
decades before and after the 1740 decree, id., at 17–19, and
nn. 35–38.
While disagreeing with New Hampshire’s understanding
of history, see Motion to Dismiss 9–14, 18–19 (compiling evi-
dence that Maine continually exercised jurisdiction over the
harbor and shipyard from the 1700’s to the present day),
Maine primarily contends that the 1740 decree and the 1977
consent judgment divided the Piscataqua River at the middle
of the main channel of navigation—a division that places
Seavey Island within Maine’s jurisdiction. Those earlier
proceedings, according to Maine, bar New Hampshire’s com-
plaint under principles of claim and issue preclusion as well
as judicial estoppel.
We pretermit the States’ competing historical claims along
with their arguments on the application vel non of the
res judicata doctrines commonly called claim and issue pre-
clusion. Claim preclusion generally refers to the effect of a
prior judgment in foreclosing successive litigation of the
very same claim, whether or not relitigation of the claim
raises the same issues as the earlier suit. Issue preclusion
generally refers to the effect of a prior judgment in foreclos-
ing successive litigation of an issue of fact or law actually
*According to New Hampshire, the Federal Government in recent years
has taken steps to close portions of the shipyard and to lease its land
and facilities to private developers. Complaint 34. New Hampshire and
Maine assert competing claims of sovereignty over private development
on shipyard lands. Ibid.

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litigated and resolved in a valid court determination essen-
tial to the prior judgment, whether or not the issue arises
on the same or a different claim. See Restatement (Second)
of Judgments §§ 17, 27, pp. 148, 250 (1980); D. Shapiro, Civil
Procedure: Preclusion in Civil Actions 32, 46 (2001). In the
unusual circumstances this case presents, we conclude that a
discrete doctrine, judicial estoppel, best fits the controversy.
Under that doctrine, we hold, New Hampshire is equitably
barred from asserting—contrary to its position in the 1970’s
litigation—that the inland Piscataqua River boundary runs
along the Maine shore.
II
“[W]here a party assumes a certain position in a legal pro-
ceeding, and succeeds in maintaining that position, he may
not thereafter, simply because his interests have changed,
assume a contrary position, especially if it be to the preju-
dice of the party who has acquiesced in the position formerly
taken by him.” Davis v. Wakelee, 156 U. S. 680, 689 (1895).
This rule, known as judicial estoppel, “generally prevents a
party from prevailing in one phase of a case on an argument
and then relying on a contradictory argument to prevail in
another phase.” Pegram v. Herdrich, 530 U. S. 211, 227, n. 8
(2000); see 18 Moore’s Federal Practice § 134.30, p. 134–62
(3d ed. 2000) (“The doctrine of judicial estoppel prevents a
party from asserting a claim in a legal proceeding that is
inconsistent with a claim taken by that party in a previous
proceeding”); 18 C. Wright, A. Miller, & E. Cooper, Federal
Practice and Procedure § 4477, p. 782 (1981) (hereinafter
Wright) (“absent any good explanation, a party should not
be allowed to gain an advantage by litigation on one theory,
and then seek an inconsistent advantage by pursuing an in-
compatible theory”).
Although we have not had occasion to discuss the doctrine
elaborately, other courts have uniformly recognized that its
purpose is “to protect the integrity of the judicial process,”
Edwards v. Aetna Life Ins. Co., 690 F. 2d 595, 598 (CA6

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1982), by “prohibiting parties from deliberately changing
positions according to the exigencies of the moment,” United
States v. McCaskey, 9 F. 3d 368, 378 (CA5 1993). See In re
Cassidy, 892 F. 2d 637, 641 (CA7 1990) (“Judicial estoppel is
a doctrine intended to prevent the perversion of the judicial
process.”); Allen v. Zurich Ins. Co., 667 F. 2d 1162, 1166 (CA4
1982) ( judicial estoppel “protect[s] the essential integrity of
the judicial process”); Scarano v. Central R. Co., 203 F. 2d
510, 513 (CA3 1953) ( judicial estoppel prevents parties from
“playing ‘fast and loose with the courts’ ” (quoting Stretch v.
Watson, 6 N. J. Super. 456, 469, 69 A. 2d 596, 603 (1949))).
Because the rule is intended to prevent “improper use of
judicial machinery,” Konstantinidis v. Chen, 626 F. 2d 933,
938 (CADC 1980), judicial estoppel “is an equitable doctrine
invoked by a court at its discretion,” Russell v. Rolfs, 893
F. 2d 1033, 1037 (CA9 1990) (internal quotation marks and
citation omitted).
Courts have observed that “[t]he circumstances under
which judicial estoppel may appropriately be invoked are
probably not reducible to any general formulation of prin-
ciple,” Allen, 667 F. 2d, at 1166; accord, Lowery v. Stovall,
92 F. 3d 219, 223 (CA4 1996); Patriot Cinemas, Inc. v. Gen-
eral Cinema Corp., 834 F. 2d 208, 212 (CA1 1987). Never-
theless, several factors typically inform the decision whether
to apply the doctrine in a particular case: First, a party’s
later position must be “clearly inconsistent” with its earlier
position. United States v. Hook, 195 F. 3d 299, 306 (CA7
1999); In re Coastal Plains, Inc., 179 F. 3d 197, 206 (CA5
1999); Hossaini v. Western Mo. Medical Center, 140 F. 3d
1140, 1143 (CA8 1998); Maharaj v. Bankamerica Corp., 128
F. 3d 94, 98 (CA2 1997). Second, courts regularly inquire
whether the party has succeeded in persuading a court to
accept that party’s earlier position, so that judicial accept-
ance of an inconsistent position in a later proceeding would
create “the perception that either the first or the second
court was misled,” Edwards, 690 F. 2d, at 599. Absent suc-

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cess in a prior proceeding, a party’s later inconsistent posi-
tion introduces no “risk of inconsistent court determina-
tions,” United States v. C. I. T. Constr. Inc., 944 F. 2d 253,
259 (CA5 1991), and thus poses little threat to judicial integ-
rity. See Hook, 195 F. 3d, at 306; Maharaj, 128 F. 3d, at 98;
Konstantinidis, 626 F. 2d, at 939. A third consideration is
whether the party seeking to assert an inconsistent position
would derive an unfair advantage or impose an unfair detri-
ment on the opposing party if not estopped. See Davis, 156
U. S., at 689; Philadelphia, W., & B. R. Co. v. Howard, 13
How. 307, 335–337 (1852); Scarano, 203 F. 2d, at 513 ( judicial
estoppel forbids use of “intentional self-contradiction . . . as
a means of obtaining unfair advantage”); see also 18 Wright
§ 4477, p. 782.
In enumerating these factors, we do not establish inflexi-
ble prerequisites or an exhaustive formula for determining
the applicability of judicial estoppel. Additional considera-
tions may inform the doctrine’s application in specific factual
contexts. In this case, we simply observe that the factors
above firmly tip the balance of equities in favor of barring
New Hampshire’s present complaint.
New Hampshire’s claim that the Piscataqua River bound-
ary runs along the Maine shore is clearly inconsistent with
its interpretation of the words “Middle of the River” during
the 1970’s litigation. As mentioned above, supra, at 747, in-
terpretation of those words was “necessary” to fixing the
northern endpoint of the lateral marine boundary, Report 43.
New Hampshire offered two interpretations in the earlier
proceeding—first agreeing with Maine in the proposed con-
sent decree that “Middle of the River” means the middle of
the main channel of navigation, and later agreeing with the
Special Master that the words mean the geographic middle
of the river. Both constructions located the “Middle of the
River” somewhere other than the Maine shore of the Pis-
cataqua River.

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Moreover, the record of the 1970’s dispute makes clear
that this Court accepted New Hampshire’s agreement with
Maine that “Middle of the River” means middle of the main
navigable channel, and that New Hampshire benefited from
that interpretation. New Hampshire, it is true, preferred
the interpretation of “Middle of the River” in the Special
Master’s report. See Exceptions and Brief for Plaintiff in
New Hampshire v. Maine, O. T. 1975, No. 64 Orig., p. 3 (here-
inafter Plaintiff ’s Exceptions) (“the boundary now proposed
by the Special Master is more favorable to [New Hampshire]
than that recommended in the proposed consent decree”).
But the consent decree was sufficiently favorable to New
Hampshire to garner its approval. Although New Hamp-
shire now suggests that it “compromised in Maine’s favor”
on the definition of “Middle of the River” in the 1970’s liti-
gation, Brief in Opposition to Motion to Dismiss 24, that
“compromise” enabled New Hampshire to settle the case, see
id., at 24–25, on terms beneficial to both States. Notably,
in their joint motion for entry of the consent decree, New
Hampshire and Maine represented to this Court that the
proposed judgment was “in the best interest of each State.”
Motion for Consent Judgment 1. Relying on that repre-
sentation, the Court accepted the boundary proposed by the
two States. New Hampshire v. Maine, 434 U. S. 1 (1977).
At oral argument, New Hampshire urged that the con-
sent decree simply fixed the “Middle of the River” at “an
arbitrary location based on the administrative convenience
of the parties.” Tr. of Oral Arg. 37. To the extent New
Hampshire implies that the parties settled the lateral marine
boundary dispute without judicial endorsement of their in-
terpretation of “Middle of the River,” that view is fore-
closed by the Court’s determination that “[t]he consent de-
cree . . . proposes a wholly permissible final resolution of
the controversy both as to facts and law,” New Hampshire
v. Maine, 426 U. S., at 368–369. Three dissenting Justices
agreed with New Hampshire that the consent decree in-

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terpreted the middle-of-the-river language “by agreements
of convenience” and not “in accordance with legal principles.”
Id., at 371 (White, J., joined by Blackmun and Stevens,
JJ., dissenting). But the Court concluded otherwise, not-
ing that its acceptance of the consent decree involved
“[n]othing remotely resembling ‘arbitral’ rather than ‘judi-
cial’ functions,” id., at 369. The consent decree “reasonably
invest[ed] imprecise terms with definitions that give effect
to [the 1740] decree,” ibid., and “[did] not fall into the cate-
gory of agreements that we reject because acceptance would
not be consistent with our Art. III function and duty,” ibid.
New Hampshire also contends that the 1977 consent de-
cree was entered without “a searching historical inquiry into
what that language [‘Middle of the River’] meant.” Tr. of
Oral Arg. 39. According to New Hampshire, had it known
then what it knows now about the relevant history, it would
not have entered into the decree. Ibid. We do not question
that it may be appropriate to resist application of judicial
estoppel “when a party’s prior position was based on in-
advertence or mistake.” John S. Clark Co. v. Faggert &
Frieden, P. C., 65 F. 3d 26, 29 (CA4 1995); see In re Corey,
892 F. 2d 829, 836 (CA9 1989); Konstantinidis, 626 F. 2d, at
939. We are unpersuaded, however, that New Hampshire’s
position in 1977 fairly may be regarded as a product of in-
advertence or mistake.
The pleadings in the lateral marine boundary case show
that New Hampshire did engage in “a searching historical
inquiry” into the meaning of “Middle of the River.” See
Reply Brief for Plaintiff in New Hampshire v. Maine, O. T.
1975, No. 64 Orig., pp. 3–9 (examining history of river bound-
aries under international law, proceedings leading up to the
1740 order of the King in Council, and relevant precedents
of this Court). None of the historical evidence cited by New
Hampshire remotely suggested that the Piscataqua River
boundary runs along the Maine shore. In fact, in attempt-
ing to place the boundary at the geographic middle of the

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river, New Hampshire acknowledged that its agents in 1740
understood the King’s order to “adjudg[e] half of the river
to” the portion of Massachusetts that is now Maine. Id., at
6 (emphasis in original) (quoting N. H. State Papers, XIX,
pp. 591, 596–597); see Reply Brief in No. 64 Orig., supra, at
4 (“The intention of those participating in the proceedings
leading to the [1740 decree] was to use ‘geographic middle’
as the Piscataqua boundary.” (emphasis in original)). In
addition, this Court independently determined that “there is
nothing to suggest that the location of the 1740 boundary
agreed upon by the States is wholly contrary to relevant evi-
dence.” New Hampshire v. Maine, 426 U. S., at 369.
Nor can it be said that New Hampshire lacked the oppor-
tunity or incentive to locate the river boundary at Maine’s
shore. In its present complaint, New Hampshire relies on
historical materials—primarily official documents and events
from the colonial and postcolonial periods, see Brief in Op-
position to Motion to Dismiss 12–19—that were no less avail-
able 25 years ago than they are today. And New Hampshire
had every reason to consult those materials: A river bound-
ary running along Maine’s shore would have placed the
northern terminus of the lateral marine boundary much
closer to Maine, “result[ing] in hundreds if not thousands
of additional acres of territory being in New Hampshire
rather than Maine,” Tr. of Oral Arg. 48 (rebuttal argument
of Maine). Tellingly, New Hampshire at the time under-
stood the importance of placing the northern terminus as
close to Maine as possible. While agreeing with the Special
Master that “Middle of the River” means geographic middle,
New Hampshire insisted that the geographic middle should
be determined by using the banks of the river, not low tide
elevations (as the Special Master had proposed), as the key
reference points—a methodology that would have placed
the northern terminus 350 yards closer to the Maine shore.
Plaintiff ’s Exceptions 3.

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Opinion of the Court
In short, considerations of equity persuade us that applica-
tion of judicial estoppel is appropriate in this case. Having
convinced this Court to accept one interpretation of “Middle
of the River,” and having benefited from that interpretation,
New Hampshire now urges an inconsistent interpretation to
gain an additional advantage at Maine’s expense. Were we
to accept New Hampshire’s latest view, the “risk of inconsist-
ent court determinations,” C. I. T. Constr. Inc., 944 F. 2d, at
259, would become a reality. We cannot interpret “Middle
of the River” in the 1740 decree to mean two different things
along the same boundary line without undermining the in-
tegrity of the judicial process.
Finally, notwithstanding the balance of equities, New
Hampshire points to this Court’s recognition that “ordi-
narily the doctrine of estoppel or that part of it which pre-
cludes inconsistent positions in judicial proceedings is not
applied to states,” Illinois ex rel. Gordon v. Campbell, 329
U. S. 362, 369 (1946). Of course, “broad interests of public
policy may make it important to allow a change of positions
that might seem inappropriate as a matter of merely pri-
vate interests.” 18 Wright § 4477, p. 784. But this is not
a case where estoppel would compromise a governmental
interest in enforcing the law. Cf. Heckler v. Community
Health Services of Crawford Cty., Inc., 467 U. S. 51, 60 (1984)
(“When the Government is unable to enforce the law be-
cause the conduct of its agents has given rise to an estoppel,
the interest of the citizenry as a whole in obedience to the
rule of law is undermined. It is for this reason that it is
well settled that the Government may not be estopped on
the same terms as any other litigant.”). Nor is this a case
where the shift in the government’s position is “the result
of a change in public policy,” United States v. Owens, 54 F. 3d
271, 275 (CA6 1995); cf. Commissioner v. Sunnen, 333 U. S.
591, 601 (1948) (collateral estoppel does not apply to Com-
missioner where pertinent statutory provisions or Treasury

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756 NEW HAMPSHIRE v. MAINE
Opinion of the Court
regulations have changed between the first and second pro-
ceeding), or the result of a change in facts essential to the
prior judgment, cf. Montana v. United States, 440 U. S. 147,
159 (1979) (“changes in facts essential to a judgment will
render collateral estoppel inapplicable in a subsequent ac-
tion raising the same issues”). Instead, it is a case between
two States, in which each owes the other a full measure of
respect.
What has changed between 1976 and today is New Hamp-
shire’s interpretation of the historical evidence concerning
the King’s 1740 decree. New Hampshire advances its new
interpretation not to enforce its own laws within its borders,
but to adjust the border itself. Given Maine’s countervailing
interest in the location of the boundary, we are unable to
discern any “broad interes[t] of public policy,” 18 Wright
§ 4477, p. 784, that gives New Hampshire the prerogative to
construe “Middle of the River” differently today than it did
25 years ago.
* * *
For the reasons stated, we conclude that judicial estoppel
bars New Hampshire from asserting that the Piscataqua
River boundary runs along the Maine shore. Accordingly,
we grant Maine’s motion to dismiss the complaint.
It is so ordered.
Justice Souter took no part in the consideration or
decision of this case.
[Appendix containing Portsmouth Harbor to Isles of
Shoals map follows this page.]

Lateral Marine Boundary Line
Maine
New Hampshire
Isles of
Shoals
Portsmouth
Harbor
Seavey
Island
Piscataqua River
Kittery
APPENDIX TO OPINION OF THE COURT
Adapted from Map 13283, Portsmouth Harbor to Isles of Shoals, National Oceanic and Atmospheric
Administration, U. S. Department of Commerce (18th ed. Nov. 2000).
Gosport
Harbor
ME
NH