I don't like provisional applications. However, you should be aware that a number of patent attorneys still recommend provisional applications. In short, opinions differ on this topic.

Provisional applications serve a very specific and narrow purpose. They came about as a patch for a specific quirk in U.S. patent law resulting from the change of a patent term from the former 17 years from the date of issue to the current 20 years from the original U.S. filing date. The quirk relates to U.S. applications claiming priority on foreign applications. To understand the purpose of provisional applications, it helps to first understand the odd quirk patched by provisional applications. For purposes of illustration, consider the following two scenarios.

Suppose Application A is filed in the U.S. on January 1, 2001 and claims no priority of any earlier filed application. Enforceability of any patent issuing on Application A would normally expire on January 1, 2021 (assuming no term extensions). Thus, the time gap between the filing date (which all prior art must pre-date) and the expiration date is twenty years.

Suppose Application B is filed in the U.S. on January 1, 2001 and claims priority of a patent application filed in Mexico on January 1, 2000. The same rules for expiration apply within the U.S, so Application B would normally expire on January 1, 2021. However, the time gap between the priority date (which all prior art must pre-date) and the expiration date is twenty-one years.

Thus, U.S. law as recently modified favors foreign inventors. So here comes the patch....

In the U.S., you can file a dummy priority application to put yourself in the same position as a foreign inventor. That dummy priority application is a provisional patent application.

Here's why I don't like provisional applications. To properly claim priority on a provisional application, the provisional application must properly support any claims in the subsequently-filed non-provisional application. However, the provisional application contains no claims. In my opinion, to properly prepare a provisional application, the claims should be drafted and the description of the provisional application should be analyzed in view of the drafted claims. The drafted claims should then be withheld for later filing.

It only makes sense to do this if you believe the value of your patent is back-end-loaded -- that the patent is more valuable at the end of its term than at the beginning. The provisional application allows the patent owner to time-shift the patent term into the future up to one year.

This is valuable generally to the pharmaceutical industry in which the lengthy FDA approval process typically delays release of a drug and in which makers of generic versions of drugs eagerly await expiration of patents. However, in most industries (particularly for new companies hoping to build a patent portfolio quickly), most of the value of a patent is front-loaded -- that is, the patent is most valuable to the patent owner at the beginning of the patent term.

Generally, outside of the pharmaceutical industry, provisional patent applications are only filed as emergency measures on the theory that a quickly thrown-together provisional application filed at the eleventh hour is better than filing nothing at all. Obviously, this should be avoided by proper planning and consulting with a patent attorney well before any planned public demonstrations, sales, or descriptions of the invention.