delivered the opinion of the Court.
This case requires us once again to reconcile the plenary-power of the States over residents within their borders with the semi-autonomous status of Indians living on tribal reservations. In this instance, the problem arises in the context of Arizona’s efforts to impose its personal income tax on a reservation Indian whose entire income derives from reservation sources. Although we have repeatedly addressed the question of state taxation of reservation Indians,
1
the problems posed by a state income tax are apparently of first impression in this Court.
2
The Arizona courts have held that such state taxation is permissible.
I
Appellant is an enrolled member of the Navajo tribe who lives on that, portion of the Nаvajo Reservation located within the State of Arizona. Her complaint al *166 leges that all her income earned during 1967 was derived from within the Navajo Reservation. Pursuant to Ariz. Rev. Stat. Ann. §43-188 (f) (Supp. 1972-1973), $16.20 was withheld from her wages for that year to cover her state income tax liability. 3 At the conclusion of the tax year, appellant filed a protest against the collection of any taxes on her income and a claim for a refund of the entire amount withheld from her wages. When no action was taken on her claim, she instituted this action in Arizona Suрerior Court on behalf of herself and those similarly situated, demanding a return of the money withheld and a declaration that the state tax was unlawful as applied to reservation Indians.
The trial court dismissed the action for failure to state a claim, and the Arizona Court of Appeals affirmed. Citing this Court’s decision in
Williams
v.
Lee,
*167
The court .then pointed to cases holding that state employees could be required to pay federal income taxes and that the State had a concomitant right to tax federal employees. See
Helvering
v.
Gerhardt,
Nor did the court find anything in the Arizona Enabling Act, 36 Stat. 557, to prevent the State from taxing reservation Indians. That Act, the relevant language of which is duplicated in the Arizona Constitution, disclaims state title over Indian lands and requires that such lands shall remain “under the absolute jurisdiction and control of the Congress of the United States.” 36 Stat. 569. But the Arizona court, relying on this Court’s decision in
Organized Village of Kake
v.
Egan,
II
It may be helpful to begin our discussion of the law applicable to this complex area with a brief statement of what this case does not involve. We are not here dealing with Indians who have left or never inhabited reservations set aside for their exclusive use or who do not possess the usual accoutrements of tribal self-govern
*168
ment. See,
e. g., Organized Village of Kake
v.
Egan, supra; Metlakatla Indian Community
v.
Egan,
The principles governing the resolution of this question are not new. On the contrary, “[t]he policy of leaving Indians free from state jurisdiction and cоntrol is deeply rooted in the Nation’s history.”
Rice
v.
Olson,
Although
Worcester
on its facts dealt with a State’s efforts to extend its criminal jurisdiction to reservation lands,
4
the rationale of the case plainly extended to state taxation within the reservation as well. Thus, in
The Kansas Indians,
It is true, as the State asserts, that some of the later Indian tax cases turn, not on the Indian sovereignty doctrine, but on whether or not the State can be said to have imposed a forbidden tax on a federal instrumentality. See,
e. g., Leahy
v.
State Treasurer of Oklahoma,
This is not to say that the Indian sovereignty doctrine, with its concomitant jurisdictional limit on the reach of state law, has remained static during the 141 years since
Worcester
was decided. Not surprisingly, the doctrine has undergone considerable evolution in response to changed circumstances. As noted above, the doctrine has not been rigidly applied in cases where Indians have left the reservation and become assimilated into the general community. See, e.
g., Oklahoma Tax Comm’n
v.
United States,
Finally, the trend has been away from the idea of inherent Indian sovereignty as a bar to state jurisdiction and toward reliance on federal pre-emption.
7
See
Mescolero Apache Tribe
v.
Jones, ante,
p. 145. The modern cases thus tend to avoid reliance on platonic notions of Indian sovereignty and to look instead to the applicable treaties and statutes which define the limits of state power. Compare,
e. g., United States
v.
Kagama,
The Indian sovereignty doctrine is relevant, then, not because it provides a definitive resolution of the issues in this suit, but because it provides a backdrop against which the applicable treaties and federal statutes must be read. It must always be remembered that the various Indian tribes were once independent and sovereign nations, and that their claim to sovereignty long predates that of our own Government. Indians today are Ameri
*173
can citizens.
9
They have the right to vote,
10
’ to use state courts,
11
and they receive some state services.
12
But it is nonetheless still true, as it was in the last century, that “[t]he relation of the Indian tribes living within the borders of the United States ... [is] an anomalous one and of a complex character. . . . Thеy were, and always have been, regarded as having a semi-independent position when they preserved their tribal relations; not as States, not as nations, not as possessed of the full attributes of sovereignty, but as a separate people, with the power of regulating their internal and social relations, and thus far not brought under the laws of the Union or of the State within whose limits they resided.”
United States
v.
Kagama,
III
When the relevant treaty and statutes are read with this tradition of sovereignty in mind, we think it clear that Arizona has exceeded its lawful authority by attempting to tax appellant. The beginning of our analysis must be with the treaty which the United States Gov- *174 eminent entered with the Navajo Nation in 1868. The agreement provided, in relevant part, that a prescribed reservation would be set aside “for the use and occupation of the Navajo tribe of Indians” and that “no persons except those herein so authorized to do, and except such officers, soldiers, agents, and employes of the government, or of the Indians, as may be authorized to enter upon Indian reservations in discharge of duties imposed by lаw, or the orders of the President, shall ever be permitted to pass over, settle upon, or reside in, the territory described in this article.” 15 Stat. 668.
The treaty nowhere explicitly states that the Navajos were to be free from state law or exempt from state taxes. But the document is not to be read as an ordinary contract agreed upon by parties dealing at arm’s length with equal bargaining positions. We have had occasion in the past to describe the circumstances under which the agreement was reached. “At the time this documеnt was signed the Navajos were an exiled people, forced by the United States to live crowded together on a small piece of land on the Pecos River in eastern New Mexico, some 300 miles east of the area they had occupied before the coming of the white man. In return for their promises to keep peace, this treaty 'set apart’ for 'their permanent home’ a portion of what had been their native country.”
Williams
v.
Lee,
It is circumstances such as these which have led this Court in interpreting Indian treaties, to adopt the general rule that “[djoubtful expressions are to be resolved in favor of the weak and defenseless people who are the wards of the nation, dependent upon its protection and good faith.”
Carpenter
v.
Shaw,
Moreover, since the signing of the Navajo treaty, Congress has consistently acted upon the assumption that the States lacked jurisdiction over Navajos living on the reservation. 13 Thus, when Arizona entered the Union, its entry was expressly conditioned on the promise that the State would “forever disclaim all right and title to . . . all lands lying within said boundaries owned or held by any Indian or Indian tribes, the right or title to which shall have been acquired through or from the United States or any prior sovereignty, and that until the title of such Indian or Indian tribes shall have been extinguished the same shall be and remain subject to the disposition and under the absolute jurisdiction and control of the Congress of the United States.” Arizona Enabling Act, 36 Stat. 569. 14
Nor is the Arizona Enabling Act silent on the specific question of tax immunity. The Act expressly provides
*176
that “nothing herein, or in the ordinance herein provided fоr, shall preclude the said State from taxing as other lands and other property are taxed any lands and other property
outside of an Indian reservation
owned or held by any Indian.”
Id.,
at 570 (emphasis added). It is true, of course, that exemptions from tax laws should, as a general rule, be clearly expressed. But we have in the past construed language far more ambiguous than this as providing a tax exemption for Indians. See,
e. g., Squire
v.
Capoeman,
Indeed, Congress’ intent to maintain the tax-exempt status of reservation Indiаns is especially clear in light of the Buck Act, 4 U. S. C. § 105
et seq.,
which provides comprehensive federal guidance for state taxation of those living within federal areas. Section 106 (a) of Title 4 U. S. C. grants to the States general authority to impose an income tax on residents of federal areas, but § 109 expressly provides that “[n]othing in sections 105 and 106 of this title shall be deemed to authorize the levy or collection of any tax on or from any Indian not otherwise taxed.” To be sure, the language of the statute itself does not make clear whether the reference to “any Indian not otherwise taxed” was intended to apply to reservation Indians earning their income on the reservation. But the legislative history makes plain that this proviso was
*177
meant to except reservation Indians from coverage of the Buck Act, see S. Rep. No. 1625, 76th Cong., 3d Sess., 2, 4 (1940); 84 Cong. Rec. 10685, and this Court has so interpreted it. See
Warren Trading Post Co.
v.
Arizona Tax Comm’n,
Finally, it should be noted that Congress has now provided a method whereby States may assume jurisdiction over reservation Indians. Title 25 U. S. C. § 1322 (a) grants the consent of the United States to States wishing to assume criminal and civil jurisdiction over reservation Indians, and 25 U. S. C. § 1324 confers upon the States the right to disregard enabling acts which limit their authority over such Indians. But the Act expressly provides that the State must act “with the consent of the tribe occupying the particular Indian country,” 25 U. S. C. § 1322 (a),
17
and must “appropriately [amend
*178
its] constitution or statutes.” 25 U. S. C. § 1324. Once again, the Act cannot be read as expressly conferring tax immunity upon Indians. But we cannot believe that Congress would have required the consent of the Indians affected and the amendment of those state constitutions which prohibit the assumption of jurisdiction if the States were free to accomplish the same goal unilaterally by simple legislative enactment. See
Kennedy
v.
District Court,
Arizona, of course, has neither amended its constitution to permit taxation of the Navajos nor secured the consent of the Indians affected. Indeed, a startling aspect of this case is that appellee apparently concedes that, in the absence of compliance with 25 U. S. C. § 1322 (a), the Arizona courts can exercise neither civil nor criminal jurisdiction over reservation Indians. See Brief for Appellee 24-26.
19
But the appellee nowhere explains how, without such jurisdiction, the State’s tax may either be imposed or collected. Cf. Tr. of Oral Arg. 38-39. Unless the State is willing to defend the position
*179
that it may constitutionally administer its tax system altogether without judicial intervention, cf.
Ward
v.
Board of County Comm’rs,
IV
When Arizona’s contentions are measured against these statutory imperatives, they are simply untenable. The State relies primarily upon language in
Williams
v.
Lee
stating that the test for determining the validity of state action is “whether [it] infringed on the right of reservation Indians to make their own laws and be ruled by them.”
In fact, we are far from convinced that when a State imposes taxes upon reservation members without their consent, its action can be reconciled with tribal self-determination. But even if the State’s premise were accepted, we reject the suggestion that the
Williams
test was meant tо apply in this situation. It must be remembered that cases applying the
Williams
test have dealt principally with situations involving non-Indians. See also
Organized Village of Kake
v.
Egan,
The problem posed by this case is completely different. Since appellant is an Indian and since her income is derived wholly from reservation sources, her activity is totally within the sphere which the relevant treaty and
*180
statutes leave for the Federal Government and for the Indians themselves. Appellee cites us to no cases holding that this legislation may be ignored simply because tribal self-government has not been infringed.
20
On the contrary, this Court expressly rejected such a position only two years ago.
21
In
Kennerly
v.
District Court,
Nor is the State’s attempted distinction between taxes on land and on income availing. Indeed, it is somewhat surprising that the State adheres to this distinction in light of our decision in Warren Trading Post Co. v. Arizona Tax Comm’n, supra, wherein we invalidated an income tax which Arizona had attempted to impose *181 within the Navajo Reservation. However relevant the land-income distinction may be in other contexts, it is plainly irrelevant when, as here, the tax is resisted because the State is totally lacking in jurisdiction over both the people and the lands it seeks to tax. In such a situation, the State has no more jurisdiction to reach income generated on reservation lands than to tax the land itself.
Finally, we cannot accept the notion that it is irrelevant “whether the . . . state income tax infringes on [appellant’s] rights as an individual Navajo Indian,” as the State Court of Appeals maintained.
Reversed.
Notes
See,
e. g., Oklahoma Tax Comm’n
v.
United States,
State courts have disagreed on the question. Compare
Ghahate
v.
Bureau of Revenue,
80 N. M. 98,
The liability was created by Ariz. Rev. Stat. Ann. § 43-102 (a) (Supp. 1972-1973) which, in relevant part, provides: “There shall be levied, collected, and paid for each taxable year upon the entire net income of every estate or trust taxable under this title and of every resident of this state and upon the entire net income of every nonresident which is derived from sources within this state, taxes in the following amounts and at the following rates upon the amount of net income in excess of credits against net income provided in §§ 43-127 and 43-128.” Appellant conceded below that she was a “resident” within the meaning of the statute, and that question, which in any event poses an issue of state law, is not now before us.
See also
Williams
v.
United States,
The federal-instrumentality doctrine does not prohibit state taxation of individuals deriving their income from federal sources. See
Graves
v.
New York ex rel. O’Keefe,
The court below distinguished
Warren Trading Post
as limited to cases where the Federal Government has pre-empted state law by regulating Indian traders in a manner inconsistent with state taxation.
The source of federal authority over Indian matters has been the subject of some confusion, but it is now generally recognized that the power derives from federal responsibility for regulating commerce with Indian tribes and for treaty making. See U. S. Const. Art. I, §8, cl. 3; Art. II, §2, cl. 2. See also
Williams
v.
Lee, 358
U. S. 217, 219 n. 4 (1959);
Perrin
v.
United States,
The extent of federal pre-emption and residual Indian sovereignty in the total absence of federal treaty obligations or legislation is therefore now something of a moot question. Cf.
Organized Village of Kake
v.
Egan,
See 8 U. S. C. § 1401 (a)(2).
See,
e. g., Harrison
v.
Laveen,
See,
e. g., Felix
v.
Patrick,
The court below pointed out that Arizona was expending tax monies for education and welfare within the confines of the Navajo Reservation. 14 Ariz, App., at 456-457,
“Congress has . . . acted consistently upon the assumption that the States have no power to regulate the affairs of Indians on a reservation. . . . Significantly, when Congress has wished the States to exercise this power it has expressly granted them the jurisdiction which
Worcester v. Georgia
has denied.”
Williams
v.
Lee,
This language is duplicated in Arizona’s own constitution. See Ariz. Const., Art. 20, ¶ 4. It is also contained in the Enabling Acts of New Mexico and Utah, the other States in which the Navajo Reservation is located. See New Mexico Enabling Act, 36 Stat. 558-559; Utah Enabling Act, 28 Stat. 108.
There is nothing in
Organized Village of Kake
v.
Egan,
See, e. g., 25 U. S. C. § 398 (congressional authorization for States to tax mineral production on unallotted tribal lahds). Cf. 18 U. S. C. § 1161 (state liquor laws may be applicable within reservations) ; 25 U. S. C. § 231 (state health and education laws may be applicable within reservations).
As passed in 1953, Pub. L. 280, 67 Stat. 588, delegated civil and criminal jurisdiction over Indian reservations to certain States, although not to Arizona. 18 U. S. C. § 1162; 28 U. S. C. § 1360. The original Act also provided a means whereby other States could аssume jurisdiction over Indian reservations without the consent of *178 the tribe affected. 67 Stat. 590. However, in 1968, Congress passed the Indian Civil Rights Act which changed the prior procedure to require the consent of the Indians involved before a State was permitted to assume jurisdiction. 25 U. S. C. § 1322 (a). Thus, had it wished to do so, Arizona could have unilaterally assumed jurisdiction over its portion of the Navajo Reservation at any point during the 15 years between 1953 and 1968. But although the State did pass narrow legislation purporting to require the enforcement of air and water pollution standards within reservations, Ariz. Rev. Stat. Ann. §§ 36-1801, 36-1865 (Supp. 1972), it declined to assume full responsibility for the Indians during the period when it had the opportunity to do so.
We do not suggest that Arizona would necessarily be empowered to impose this tax had it followed the procedures outlined in 25 U. S. C. § 1322 et seq. Cf. 25 U. S. C. § 1322 (b). That question is not presently before us, and we express no views on it.
In light of our prior cases, appellee has no choice but to make this concession. See,
e. g., Kennedy
v.
District Court,
Organized, Village of Kake
v.
Egan,
Indeed, the position was expressly rejected in
Williams
itself, upon which appellee so heavily relies.
Williams
held that
“absent governing Acts of Congress,
the question has always been whether the state action infringed on the right of reservation Indians to make their own laws and be ruled by them.”
