Mr. Chief Justice Stone
delivered the opinion of the Court.
In this patent infringement suit the question is whether the assignor of a patent is estopped by virtue of his assignment to defend a suit for infringement of the assigned patent on the ground that the alleged infringing device is that of a prior art, expired patent.
Automatic Paper Machinery Company, Inc., petitioner’s assignor, acquired by assignment, from respondent Marcalus, Patent No. 1,843,429 of February 2,1932, issued on the application of Marcalus for “a method and machine for mounting a cutting strip of a hard non-metallic substance on an edge of a box blank.” The patent describes and claims a method, and a machine for employing it, whereby, in substantially one operation, indurated paper is drawn from a roll and brought into overlapping relationship with the edge of a box blank, when a strip of the paper is automatically cut off and glued to the box blank in such position that its longitudinal edge projects beyond the edge of the box blank. The box thus equipped with the cutting edge of the strip is useful as a dispensing container for rolled wax paper which, as drawn from the roll, may be cut in any desired lengths by drawing it across the [251]*251cutting edge at an angle with the plane of the cutter. Marcalus, while an officer and employee of petitioner, made the patented invention and assigned his patent application to petitioner for a valuable consideration. The patent issued on the application as filed, without amendment, after which Marcalus severed his connection with petitioner and organized respondent company, which he controls, and which, like petitioner, is engaged in producing and selling box blanks having a cutting edge.
In the present suit, brought by petitioner for infringement of the assigned patent, respondents defended on the ground that their accused machine is a copy of that of the expired, prior art patent issued to Inman in 1912. The District Court gave judgment for petitioner, 54 F. Supp. 105, holding that inasmuch as respondents were estopped by Marcalus’ assignment of the patent to show its invalidity, they could not, by recourse to the prior art to show noninfringement, accomplish the same result by indirection. The Court of Appeals reversed, 147 F. 2d 608, holding that the prior art may be resorted to by the assignor to measure the extent of anticipation for the purpose of limiting the claims of the assigned patent, and thus avoid infringement. Because of the identity patent-wise of the Inman patent with the assigned patent and with the accused device, the court held that the claims of the assigned patent were limited to naught, and hence that there could be no infringement.
To sustain its right to enjoin infringement by the assignor of a patented invention anticipated by a prior art patent, petitioner relies on the doctrine of estoppel as applied to the assignor of a patent for value. Its basic principle is said to be one of good faith, that one who has sold his invention may not, to the detriment of the purchaser, deny the existence of that which he has sold. See Westinghouse Co. v. Formica Co., 288 F. 330, 333. The rule, as stated by this Court in Westinghouse Co. v. For[252]*252mica Co., 266 U. S. 342, 349, is “that an assignor of a patent right is estopped to attack the utility, novelty or validity of a patented invention which he has assigned or granted as against any one claiming the right under his assignment or grant. As to the rest of the world, the patent may have no efficacy and create no right of monopoly; but the assignor can not be heard to question the right of his assignee to exclude him from its use. Curran v. Burdsall, 20 Fed. 835; Ball & Socket Fastener Co. v. Ball Glove Fastening Co., 58 Fed. 818; Woodward v. Boston Lasting Machine Co., 60 Fed. 283, 284; Babcock v. Clarkson, 63 Fed. 607; Noonan v. Chester Park Athletic Co., 99 Fed. 90, 91.”
Respondents, denying that the doctrine of estoppel can rightly be applied to patent assignments, also insist that the present case is not within the scope of the doctrine. Compare Buckingham Products Co. v. McAleer Mfg. Co., 108 F. 2d 192 with Casco Products Corp. v. Sinko Tool & Mfg. Co., 116 F. 2d 119. Both parties rely on the decision of this Court in the Formica case, supra, which, although stating that the assignor cannot deny the novelty and validity of the assigned patented invention, nevertheless held that the claims of a patent may be narrowed by reference to the prior art so as to restrict them to so much of the invention described by the specifications as is not exhibited by the prior art. Klein v. Russell, 19 Wall. 433, 466, 467; Garneau v. Dozier, 102 U. S. 230; Wollensak v. Reiher, 115 U. S. 87; Beidler v. United States, 253 U. S. 447; Mackay Co. v. Radio Corp., 306 U. S. 86, 94. Cf. Hocking & Co. v. Hocking, 4 R. P. C. 255, 434, 6 R. P. C. 69; Clark v. Adie, 2 App. Cas. 423; Crosthwaite v. Steel, 6 R. P. C. 190.
This Court in the Formica case, passing the question, not present here, whether the estoppel of the assignor extends to claims added by the assignee to the application in the Patent Office, held that the estoppel did not, in any [253]*253event, preclude the assignor charged as an infringer from narrowing or qualifying their construction by reference to the prior art, saying, 266 U. S. at 351: “The distinction may be a nice one but seems to be workable.” It accordingly, by reference to the prior art, interpreted the claims, by narrowing them to a two-step process, shown by the specifications, which the court found to be the assignor’s advance over the prior art, but which was not in terms embodied in the claims. The Court thus sustained the defense of noninfringement by restricting the claims by reference to the prior art, and by holding in effect that the invention assigned was not as broad in scope as the claims would otherwise on their face define it to be.
Petitioner, pointing to the logical embarrassment in applying a doctrine which forbids the assignor to deny validity of the patented invention for want of novelty, but nevertheless allows him to narrow its scope by reference to the prior art in order to save his accused device from infringement, insists that the court below has resorted to the prior art, not for the purpose of narrowing the claims and distinguishing from the prior art something which the assignor invented, but for the purpose of destroying the claims because anticipated. This is said to be precisely the same in purpose and effect as to deny invention for want of novelty. It is urged that the permission thus given to respondent assignor to show want of novelty which he is estopped to deny, is to disregard the estoppel by which, by hypothesis, he is bound.
Respondents, on the other hand, insist that a literal application of the rule of the Formica
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Mr. Chief Justice Stone
delivered the opinion of the Court.
In this patent infringement suit the question is whether the assignor of a patent is estopped by virtue of his assignment to defend a suit for infringement of the assigned patent on the ground that the alleged infringing device is that of a prior art, expired patent.
Automatic Paper Machinery Company, Inc., petitioner’s assignor, acquired by assignment, from respondent Marcalus, Patent No. 1,843,429 of February 2,1932, issued on the application of Marcalus for “a method and machine for mounting a cutting strip of a hard non-metallic substance on an edge of a box blank.” The patent describes and claims a method, and a machine for employing it, whereby, in substantially one operation, indurated paper is drawn from a roll and brought into overlapping relationship with the edge of a box blank, when a strip of the paper is automatically cut off and glued to the box blank in such position that its longitudinal edge projects beyond the edge of the box blank. The box thus equipped with the cutting edge of the strip is useful as a dispensing container for rolled wax paper which, as drawn from the roll, may be cut in any desired lengths by drawing it across the [251]*251cutting edge at an angle with the plane of the cutter. Marcalus, while an officer and employee of petitioner, made the patented invention and assigned his patent application to petitioner for a valuable consideration. The patent issued on the application as filed, without amendment, after which Marcalus severed his connection with petitioner and organized respondent company, which he controls, and which, like petitioner, is engaged in producing and selling box blanks having a cutting edge.
In the present suit, brought by petitioner for infringement of the assigned patent, respondents defended on the ground that their accused machine is a copy of that of the expired, prior art patent issued to Inman in 1912. The District Court gave judgment for petitioner, 54 F. Supp. 105, holding that inasmuch as respondents were estopped by Marcalus’ assignment of the patent to show its invalidity, they could not, by recourse to the prior art to show noninfringement, accomplish the same result by indirection. The Court of Appeals reversed, 147 F. 2d 608, holding that the prior art may be resorted to by the assignor to measure the extent of anticipation for the purpose of limiting the claims of the assigned patent, and thus avoid infringement. Because of the identity patent-wise of the Inman patent with the assigned patent and with the accused device, the court held that the claims of the assigned patent were limited to naught, and hence that there could be no infringement.
To sustain its right to enjoin infringement by the assignor of a patented invention anticipated by a prior art patent, petitioner relies on the doctrine of estoppel as applied to the assignor of a patent for value. Its basic principle is said to be one of good faith, that one who has sold his invention may not, to the detriment of the purchaser, deny the existence of that which he has sold. See Westinghouse Co. v. Formica Co., 288 F. 330, 333. The rule, as stated by this Court in Westinghouse Co. v. For[252]*252mica Co., 266 U. S. 342, 349, is “that an assignor of a patent right is estopped to attack the utility, novelty or validity of a patented invention which he has assigned or granted as against any one claiming the right under his assignment or grant. As to the rest of the world, the patent may have no efficacy and create no right of monopoly; but the assignor can not be heard to question the right of his assignee to exclude him from its use. Curran v. Burdsall, 20 Fed. 835; Ball & Socket Fastener Co. v. Ball Glove Fastening Co., 58 Fed. 818; Woodward v. Boston Lasting Machine Co., 60 Fed. 283, 284; Babcock v. Clarkson, 63 Fed. 607; Noonan v. Chester Park Athletic Co., 99 Fed. 90, 91.”
Respondents, denying that the doctrine of estoppel can rightly be applied to patent assignments, also insist that the present case is not within the scope of the doctrine. Compare Buckingham Products Co. v. McAleer Mfg. Co., 108 F. 2d 192 with Casco Products Corp. v. Sinko Tool & Mfg. Co., 116 F. 2d 119. Both parties rely on the decision of this Court in the Formica case, supra, which, although stating that the assignor cannot deny the novelty and validity of the assigned patented invention, nevertheless held that the claims of a patent may be narrowed by reference to the prior art so as to restrict them to so much of the invention described by the specifications as is not exhibited by the prior art. Klein v. Russell, 19 Wall. 433, 466, 467; Garneau v. Dozier, 102 U. S. 230; Wollensak v. Reiher, 115 U. S. 87; Beidler v. United States, 253 U. S. 447; Mackay Co. v. Radio Corp., 306 U. S. 86, 94. Cf. Hocking & Co. v. Hocking, 4 R. P. C. 255, 434, 6 R. P. C. 69; Clark v. Adie, 2 App. Cas. 423; Crosthwaite v. Steel, 6 R. P. C. 190.
This Court in the Formica case, passing the question, not present here, whether the estoppel of the assignor extends to claims added by the assignee to the application in the Patent Office, held that the estoppel did not, in any [253]*253event, preclude the assignor charged as an infringer from narrowing or qualifying their construction by reference to the prior art, saying, 266 U. S. at 351: “The distinction may be a nice one but seems to be workable.” It accordingly, by reference to the prior art, interpreted the claims, by narrowing them to a two-step process, shown by the specifications, which the court found to be the assignor’s advance over the prior art, but which was not in terms embodied in the claims. The Court thus sustained the defense of noninfringement by restricting the claims by reference to the prior art, and by holding in effect that the invention assigned was not as broad in scope as the claims would otherwise on their face define it to be.
Petitioner, pointing to the logical embarrassment in applying a doctrine which forbids the assignor to deny validity of the patented invention for want of novelty, but nevertheless allows him to narrow its scope by reference to the prior art in order to save his accused device from infringement, insists that the court below has resorted to the prior art, not for the purpose of narrowing the claims and distinguishing from the prior art something which the assignor invented, but for the purpose of destroying the claims because anticipated. This is said to be precisely the same in purpose and effect as to deny invention for want of novelty. It is urged that the permission thus given to respondent assignor to show want of novelty which he is estopped to deny, is to disregard the estoppel by which, by hypothesis, he is bound.
Respondents, on the other hand, insist that a literal application of the rule of the Formica case limits the claims of the assigned patent to a structure having certain minor mechanical additions made by Marcalus to the machine of the Inman patent which respondents copied by their accused device. These additions, it is conceded, may not involve invention, but if so, it is said, respondents are estopped to assert it. And applying the rule of' the [254]*254Formica case they urge that the claims of the patent may nevertheless be narrowed to a machine embodying the additional, minor features not found in the Inman machine, and infringement may thus be avoided.
But in the circumstances of this case we find it unnecessary to pursue these logical refinements, or to determine whether, as respondent asks, the doctrine of estoppel by patent assignment as stated by the Formica case should be rejected. To whatever extent that doctrine may be deemed to have survived the Formica decision or to be restricted by it, we think that case is not controlling here. For other considerations are dispositive of this case, in which, unlike Formica, the accused machine is precisely that of an expired patent. Neither in that case nor in any other, so far as we are advised, was the doctrine of estoppel applied so as to penalize the use of the invention of an expired patent. That we think is foreclosed by the patent laws themselves.
Revised Statutes, §§ 4886, 4884 as amended, 35 U. S. C. §§ 31, 40, provide for the grant of a patent for a term of seventeen years to any person who has invented a “new and useful art, machine, manufacture, or composition of matter.” The grant is conditioned upon the filing of an application in the Patent Office describing the invention and the manner of making and using it. R. S. § 4888 as amended, 35 U. S. C. § 33. Revised Statutes, §§ 4895, 4898, 35 U. S. C. §§ 44, 47, authorize the assignment of an invention while the application for a patent is pending and of the patent rights to the invention after the patent has issued. Section 24 (7) of the Judicial Code, 28 U. S. C. § 41 (7), confers on district courts of the United States jurisdiction of cases arising under the patent laws, and R. S. § 4921 as amended, 35 U. S. C. § 70, gives the district courts authority to entertain suits to restrain infringement and for recovery of any resulting damage from the infringement of any right secured by the patent grant. ■
[255]*255The enactment of these provisions is the mode by which Congress has chosen to carry into effect the policy sanctioned by the Constitution, Article I, § 8, Cl. 8 “To promote the Progress of Science and useful Arts, by securing for limited Times to . . . Inventors the exclusive Right to their . . . Discoveries.” The nature and extent of the legal consequences of the expiration of a patent are federal questions, the answers to which are to be derived from the patent laws and the policies which they adopt. Cf. Sola Electric Co. v. Jefferson Co., 317 U. S. 173, 176; Steele v. L. & N. R. Co., 323 U. S. 192, 204, and cases cited. By the patent laws Congress has given to the inventor opportunity to secure the material rewards for his invention for a limited time, on condition that he make full disclosure for the benefit of the public of the manner of making and using the invention, and that upon the expiration of the patent the public be left free to use the invention. See Special Equipment Co. v. Coe, 324 U. S. 370, 378. As has been many times pointed out, the means adopted by Congress of promoting the progress of science and the arts is the limited grant of the patent monopoly in return for the full disclosure of the patented invention and its dedication to the public on the expiration of the patent. Grant v. Raymond, 6 Pet. 218, 241-242; Gill v. Wells, 22 Wall. 1; Bauer v. O’Donnell, 229 U. S. 1; Motion Picture Co. v. Universal Film Co., 243 U. S. 502, 510-511, and cases cited.
The aim of the patent laws is not only that members of the public shall be free to manufacture the product or employ the process disclosed by the expired patent, but also that the consuming public at large shall receive the benefits of the unrestricted exploitation, by others, of its disclosures. Kellogg Co. v. National Biscuit Co., 305 U. S. 111, 117-120. If a manufacturer or user could restrict himself, by express contract, or by any action which would give rise to an “estoppel,” from using the invention of an [256]*256expired patent, he would deprive himself and the consuming public of the advantage to be derived from his free use of the disclosures. The public has invested in such free use by the grant of a monopoly to the patentee for a limited time. Hence any attempted reservation or continuation in the patentee or those claiming under him of the patent monopoly, after the patent expires, whatever the legal device employed, runs counter to the policy and purpose of the patent laws. And for the same reason a stranger, such as respondent Marcalus, cannot, by securing and assigning a patent on the invention of the expired Inman patent, confer on petitioner any right to deprive the public of the benefits of the free use of the invention for which the public has paid by the grant of a limited monopoly.
By the force of the patent laws not only is the invention of a patent dedicated to the public upon its expiration, but the public thereby becomes entitled to share in the good will which the patentee has built up in the patented article or product through the enjoyment of his patent monopoly. Hence we have held that the patentee may not exclude the public from participating in that good will or secure, to any extent, a continuation of his monopoly by resorting to the trademark law and registering as a trademark any particular descriptive matter appearing in the specifications, drawings or claims of the expired patent, whether or not such matter describes essential elements of the invention or claims. Kellogg Co. v. National Biscuit Co., supra, 117-120; Singer Manufacturing Co. v. June Manufacturing Co., 163 U. S. 169, 185.
It is thus apparent that the patent laws preclude the patentee of an expired patent and all others including petitioner from recapturing any part of the former patent monopoly; for those laws dedicate to all the public the ideas and inventions embodied in an expired patent. They do not contemplate that anyone by contract or any [257]*257form of private arrangement may withhold from the public the use of an invention for which the public has paid by its grant of a monopoly and which has been appropriated to the use of all. The rights in the invention are then no longer subject to private barter, sale, or waiver. Cf. Phillips Co. v. Grand Trunk R. Co., 236 U. S. 662; Midstate Horticultural Co. v. Pennsylvania R. Co., 320 U. S. 356, 361; Brooklyn Bank v. O’Neil, 324 U. S. 697, 704. It follows that the patent laws preclude the petitioner assignee from invoking the doctrine of estoppel, as a means of continuing as against respondent, his assignor, the benefit of an expired monopoly, and they preclude the assignor from estopping himself from enjoying rights which it is the policy of the patent laws to free from all restrictions. For no more than private contract can estoppel be the means of successfully avoiding the requirements of legislation enacted for the protection of a public interest. Compare Pittsburgh, C., C. & St. L. R. Co. v. Fink, 250 U. S. 577, 583 with Louisville & Nashville R. Co. v. Mottley, 219 U. S. 467, 476-477; New York Central & H. R. R. Co. v. Gray, 239 U. S. 583, 586-587; Norman v. B. & O. R. Co., 294 U. S. 240, 304-305, 309-310, and cases cited. The interest in private good faith is not a universal touchstone which can be made the means of sacrificing a public interest secured by an appropriate exercise of the legislative power. The patent laws preclude us from saying that the patent assignment, which they authorize, operates to estop the assignor from asserting that which the patent laws prescribe, namely, that the invention of an expired patent is dedicated to the public, of which the assignor is a member.
The judgment is affirmed for the reason that we find that the application of the doctrine of estoppel so as to foreclose the assignor of a patent from asserting the right to make use of the prior art invention of an expired patent, which anticipates that of the assigned patent, is incon[258]*258sistent with the patent laws which dedicate to public use the invention of an expired patent. The assignor has a complete defense to an action for infringement where the alleged infringing device is that of an expired patent.
We have no occasion to consider the question discussed in briefs and arguments of counsel, whether the estoppel by patent assignment violates either the terms or policy of the laws against restraints of trade and competition.
Affirmed.
Mr. Justice Reed
considers that the dominant rule of Westinghouse Co. v. Formica Co., 266 U. S. 342, 349, is “that an assignor of a patent right is estopped to attack the utility, novelty or validity of a patented invention which he has assigned or granted as against any one claiming the right under his assignment or grant.” The fact that the prior art is evidenced by an expired patent does not seem significant to him. Consequently he would reverse.
Mr. Justice Jackson took no part in the consideration or decision of this case.
This question was not raised or argued in Westinghouse Co. v. Formica Co., supra, nor, so far as appears, in any of the cases cited in that opinion or the English cases which preceded it.
By § 515 of the Restatement of Contracts, a restraint of trade is unreasonable and hence unlawful if it "is based on a promise to refrain from competition and is not ancillary either to a contract for the transfer of good will or other subject of property . . .” See generally as to the validity of contracts not to compete 76 Pa. L. Rev. 244, 257 if.; Handler, Cases and Materials on Trade Regulation, 102-150.