Ask Patents is a question and answer site for people interested in improving and participating in the patent system. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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, 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.

share|improve this question
up vote 4 down vote accepted

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.

share|improve this answer
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 Jan 24 '14 at 20:31
I think the idea was Y predates X in the example. – Micah Siegel Jan 24 '14 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 Jan 24 '14 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 Jan 24 '14 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 – HTH Aug 12 '14 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 for the details (I also posted a longer answer to this question on

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.