Provisional patent applications do not require claims or a declaration of the inventor, and they require about a filing fee which is much less than for a regular patent application. 

The provisional patent application does not start the 20-year-from-filing term, but it can be relied on for priority in a later, complete, patent application filed within a year (but only to the extent of what it discloses). 

Under the Paris Convention, the provisional patent application can be relied on for priority in foreign countries as well.

A provisional application is not a substitute for a full patent application  – rather, it is to be used in conjunction with a regular, full patent application. 

A provisional application can be useful for: 

(1) establishing an early priority date for full patent applications (the U.S. and most foreign countries have a “first-to-file” rule – if several different inventors file patent applications on the same invention, the inventor with the earliest priority date typically gets a patent – in the US in some instances an early public disclosure can be relied on for priority in a patent application filed within a year); 

(2)  insuring to some extent against unknown potentially patent-barring events (such as an offer of sale, a public use, or a publication or disclosure anywhere in the world describing the invention) which may occur after the provisional patent application is filed, but before the full patent application is filed; 

(3)  effectively extending the term of a U.S. patent by one year (from 20 to 21 years); 

(4)  allowing an inventor who has no interest in foreign patents to mark his invention “patent pending” while he markets it;  and

(5)  insuring to some extent against potentially patent-barring events (such as an offer of sale, a public use, or a publication or disclosure anywhere in the world describing the invention) made by or through the inventor which may occur less than a year before the provisional patent application is filed, but more than a year before the full patent application is filed.

Provisional patent applications are not examined;  they are automatically abandoned one year from the date of filing. 

If the invention is not fully supported and disclosed in a provisional application, that provisional application may be of little or no value.  A provisional application prepared by an inventor should never take the place of a complete, attorney-prepared patent application.  If the provisional application is missing critical written description or detail in the drawings, it may not be sufficient to afford priority to the inventor in a later patent application.  The more complete a provisional patent application is, the more useful it is.  Ideally, a provisional patent application would contain as much information as a regular, full patent application.

If patent protection based on the provisional patent application is desired, within a year of the filing date of the provisional application, a full patent application describing and claiming the invention must be filed.  In order to assure that foreign patent rights are preserved, it is preferable that the full patent application be filed before any non-confidential disclosure of the invention is made.  If the invention was disclosed non-confidentially or put on sale before the provisional application was filed, then the full application should be filed within a year of the date of the disclosure or placing on sale.

An inventor who wishes to get patent pending protection for his invention as quickly as possible would: (1)  immediately file a provisional patent application;  (2)  quickly have an expedited patentability search run;  (3)  have a more extensive patent application, which takes into account the results of the patentability search, prepared and filed on an expedited basis;  and (4)  file a PCT application and perhaps other foreign applications within a year of the provisional patent application filing date.  Depending in part upon the technology involved, the activity in that technological field, the inventor’s resources, and the potential value of the invention, such a course of action can range from extremely prudent to bordering on extravagant.  This is not a recommended course of action for everyone –  however, everyone should be aware of this possibility so that an informed decision to forego it can be made.