There are many different U.S. patent application types. These application types may be used under a wide variety of circumstances. The trick is to learn when to use which application. 

In this section, we will discuss the two parent application types, the nonprovisional and the provisional application. We refer to these as parent applications because they may be filed first, without any other preceding application. Subsequent or offspring applications are those that are filed after a parent application (nonprovisional and provisional) has been filed.

Provisional applications
Provisional applications do not require claims. They require a cover sheet identifying the application as a provisional application, a specification, drawings (where necessary) and a fee. In addition, they are never examined or even sent to an examiner. Instead, they expire after 12 months, no matter what.  Provisional applications are filed to hold the idea behind the invention until the inventor has the time and/or the money to file a regular, nonprovisional application. If a regular, nonprovisional application is filed before the 12 month expiration of the provisional, then the nonprovisional application will receive the earlier provisional filing date.