I am creating a wiki for the answer(s), please feel free to update below each question as appropriate. If you have a second answer, number it accordingly and place it below other answers. **For (a) an application that has NOT yet been issued, sub-questions:** > (1) Does the NEW application cancel the previous (original) application, taking its priority (filing) date? If the new application is defeated/rejected, does their original application come back to life or is it also lost? A continuation does not necessarily mean the original application is dead. Just like any other application, it may be rejected, or the applicant may abandon it, or it may issue as a patent. The continuation likewise, so it's possible that both the original application and the continuation would result in (separate) patents being issued. > (2) Does a significant change in the continuation application mean that the original application(s) was/were flawed and/or incomplete? How does this affect the new patent application credibility? No, it doesn't mean the original was necessarily flawed or incomplete. > (3) Assuming the continued application builds upon the prior application (ergo, requiring prior art pertaining to original claims to predate the previous filing date), how does prior art on ADDED or CHANGED items affect the application, i.e. does prior art for new/changed claims also need to predate the ORIGINAL filing date? At least normally, a continuation gets the priority date of the first application from which it is derived (i.e., in some cases, you can have a continuation of a continuation of a continuation in part of a ..., going on for years). Just for one example, US Patent 6,442,336 says: > This application is a continuation of application Ser. No. 08/110,861, filed Aug. 24, 1993, now U.S. Pat. No. 5,446,599 which is a division of application Ser. No. 07/818,168, filed Jan. 8, 1992, now U.S. Pat. No. 5,260,837, which is a division of application Ser. No. 07/325,768, filed Mar. 20, 1989, abandoned, which is a continuation-in-part of application Ser. No. 06/877,319, filed Jun. 23, 1986, now U.S. Pat. No. 4,819,101, which is a continuation of application Ser. No. 06/516,532, filed Jul. 25, 1983, now U.S. Pat. No. 4,604,668, which is a continuation of application Ser. No. 06/209,057, filed Nov. 21, 1980, abandoned. ---------- **For (b) an issued patent that HAS expired:** > (1) Can a continuation patent be filed for an expired patent? I do not believe an expired patent can be used for continuation. ---------- **For (c) an issued patent that has NOT expired, sub-questions:** > (1) Can a trivial change be used to simply extend the life of the patent, indefinitely by applying trivial changes periodically? Is there a solid litmus test for this or is it just up to the examiners? Yes and no. You can continue an *application*, but only while that application remains in prosecution (i.e., before it issues as a patent). Under the old patent expiration model (i.e., that patents were valid for 17 years after being issued) yes, it was possible to extend the life of a patent for quite a while by writing continuations, contiuations-in-part, divisions, etc. Under the current system (that a patent expires 20 years after application) this has been drastically reduced, if not eliminated entirely, because (at least normally) the date of the *original* application will be used to compute the expiration date of a continuation. > (2) Can a major change that effectively turns the invention into something else be introduced periodically, resulting in indefinite continuations by simply writing in or incorporating new technologies as they come out, thus broadening the scope of the original invention (to the point where it covers completely different industries/areas)? It's not supposed to happen -- the original specification is supposed to support whatever is claimed in a continuation, continuation-in-part or a divisional application. That said, people have certainly *tried* to "stretch" an application to cover newer technologies. Just for example, Jerome Lemelson (the inventor on the patent quoted above) once wrote a patent on a "computer system". After TI came out with the first microcontroller (i.e., essentially a complete computer system on a single integrated circuit), Mr. Lemelson wrote a continuation of one of his earlier patents that added something to the effect that: "...and all of it is on one integrated circuit". The patent issued, but was eventually invalidated -- the court found that the original specification contained no support for the idea of the whole system being on a single integrated circuit, so the TI team (Gary Boone, and, if memory serves, a few others) officially invented the microcontroller. > (3) If a continuation patent is found to be invalid, how does that affect the original (built upon) patent(s)? They're independent patents -- each is valid or invalid on its own. That said, if (for example) the parent patent were found invalid due to insufficient teaching of the patented invention, there's probably an increased chance that the same would be true of any derived patents as well.