From what I've been reading about US patents, once a patent has expired, it enters the public domain and can be freely used.

The patent I was looking at was filed on 1/1999 and published in 10/2000. So, obviously the 20-year patent term has not yet be reached. However, the status appears to be expired due to non-payment of the maintenance fee.

On google patents, the status is:

12/2008 Expired due to failure to pay maintenance fee

On uspto.gov, the patent's status is shown as:

Patent Expired Due to NonPayment of Maintenance Fees Under 37 CFR 1.362

Has the patent entered the public domain and can it be used freely?

Additionally (and assuming that it is in the public domain), can someone come along at some point and start paying the maintenance fee again and pull it out of the public domain until the 20-year term is reached? It is very unlikely that this patent will be revived by the company that originally filed it since they shut down production of products using the patent in 2000 and moved onto other things.

3 Answers 3


Two or three issues involved with this. A patent that expired due to non-payment of maintance fee can be revived by petition as either unintentional or unavoidable. Unintentional has a two-year limit and unavoidable is very hard to establish. Only the patent owner can file these, not just anyone who comes along. Even if revived there are intervening rights (after the 6 mo. grace period) to anyone who started practicing the patent while it was dead to keep doing what they were doing.

All of this pertains to the claimed subject matter. Anything taught in the patent that was never claimed is "dedicated to the public" right away. Of course something taught but not claimed in patent X might very well be patented in some other patent Y.

  • George, your answer intuitively sounds correct, and from what I know off the top of my head, the unintentional/unavoidable bit is correct, but I just wanted to clarify the last sentence. If something is taught in patent X, sufficiently to enable someone to practice, than by definition wouldn't that invention not be patentable in patent Y due to anticipation?
    – user7726
    Commented Jan 24, 2014 at 20:31
  • I think the idea was Y predates X in the example. Commented Jan 24, 2014 at 20:56
  • Yes, Y could have been the subject of a completely different patent by a completely different inventor that has an earlier priority date. If the same inventor, Y could be a year later than X. Also, there could be a family of patents, all getting priority back to a common original disclosure. Technologies A and B are taught in the specification and two patents result, one with claims to A and the other with claims to B. A non-payment of maintenance fees or even all claims killed in a re-exam for one patent doesn't affect the other patent (unless they are linked by a terminal disclaimer.)
    – George White
    Commented Jan 24, 2014 at 21:17
  • @Max - There are also cases where a patentee gets very similar but not identical claim wording allowed in two separate patents. If the second one gets a non-statutory double patenting rejection and a terminal disclaimer is filed then when one patent dies, they both die. This may not be the case in all instances and a patent with slightly different limitations may still be alive after its brother expires due to maintenance fee non-payment.
    – George White
    Commented Jan 24, 2014 at 21:38
  • George - just for edification, they recently changed the rule to get rid of the two-year limit. See Patent Law Treaties Implementation Act of 2012, Pub. L. No. 112-211, 126 Stat. 1527; see also 35 U.S.C. § 41(c)(1). 35 U.S.C. § 27; and 37 C.F.R. 1.137. There's a good summary of this at clm.com/publication.cfm?ID=489.
    – HTH
    Commented Aug 12, 2014 at 17:22

If you're sure that the patent has really expired, then the specific invention in the patent is no longer patent-protected, so the patent holder can't sue over it. However, make sure of this, because figuring out when a patent has really expired can be complicated.

Additionally, keep in mind that patents can overlap, which means that even if that one specific patent you're looking at has expired, there may still be other patents out there that will block some features, or maybe all features, of the invention that you were thinking about using or selling.

Lastly, you asked if someone can restore a patent that has expired due to failure to pay the maintenance fees (although "lapsed" or "abandoned" might be a more technically accurate term). The answer is yes. See http://www.clm.com/publication.cfm?ID=489 for the details (I also posted a longer answer to this question on https://patents.stackexchange.com/a/10031/11213).


It is important to remember that a patent does not give anybody the right to do what the patent covers. For example, if I had a patent on a more effective delivery system for MDMA or LSD, having a patent doesn't change the fact that those drugs are considered Schedule 1 and illegal under almost every circumstance -- meaning that my delivery system couldn't be used even though I had a patent on it.

While a patent doesn't give the patentee the right to practice the invention, it does give them the right to sue people to stop them from using the invention (or to recover financial damages). The expiration of a patent simply means that the owner of that patent can no longer sue anybody for using the inventions claimed in the patent.

Those things together mean that the concept of "public domain" for a patent is quite limited. Taking the game "monopoly" as an example, the game was initially covered by a patent, by copyright, and by trademark law (though it does seem likely that recent Supreme Court decisions may have rendered that game not patentable today). When the patent expired, the copyright and trademark in the game remained in place. So while a company could sell a game with the same game-play mechanics that were claimed in the patent without fear of being sued for infringing the patent, that company could still be sued if they violate the copyright to the game or call it "Monopoly", despite the trademark.

The bottom line is that the expiration of a patent simply means that the patent is no longer in play (subject to the revival issues discussed in other answers). However, there are other intellectual property rights (copyright, trade secret, trademark, trade dress, state-level trademarks, rights of publicity, etc.) that can give rise to significant liability. The expiration of the patent will not impact those other rights. The mere expiration of a patent does not mean that anybody can freely practice everything in the patent until they are satisfied (preferably by a lawyer's opinion letter) that what they intend to do is (a) legal, and (b) does not violate any other IP rights.

The other thing about patents is that it is common for a single patent application to result in numerous patents. There is even a thing called a "terminal disclaimer" that is used when a second patent claims something not significant different than the first patent. Because patent maintenance fees are expensive, infrequently a patent owner will allow one patent to go expired for non-payment of fees, counting on other patents in the family to cover the same material. You'll want to go to https://portal.uspto.gov/pair/PublicPair and look up the expired patent. First, make sure it is really expired. Second, check the "continuity" tab and see if there are other patents still in force (or pending applications) in that patent family.

Perhaps most importantly, you need to seek proper legal advice. A good IP lawyer should be able to walk you through it. It is tough to answer this in the abstract, and the facts specific to what you want to do will be critical in having a lawyer give you the right answer.

  • 1
    Yes, I believe this is an important correctly informative answer. Expiry of one patent doesn't necessarily affect any other form of right affecting freedom-to-use. As gary-s says, such other rights can take a variety of forms. Freedom-to-use investigations become hardly less necessary just because of expiry of one right. Such investigations can become expensive, in real life some users decide to rely on their own prior knowledge of the extent of rights in their field. Lawyers have to be cautious and call this legally risky, but the extent of the risk taken is up to the client.
    – terry-s
    Commented Mar 13, 2019 at 20:54

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