What is a provisional application?
In March 2013 the US adopted a first-to-file system. Basically, that means in a race to the patent office; whoever files first gets the patent. A provisional patent application allows an inventor to file quickly, without having to meet all the requirements of a formal utility patent application. It is only a first step, but it gives a one year window during which an applicant can file a formal application. If no formal application is filed during that period, the priority is lost.
Although provisionals can be extremely short- perhaps only a few sentences and a couple drawings, and can omit the usual sections such as Background, Brief Description of the Drawings, and so forth, they must still satisfy the enablement, best mode, and written description requirements of a utility application.
Although not required, it is a very good idea to include at least some claims in a provisional.
One critical word of warning. The inventor gets priority only for what is disclosed in the provisional. For new material added in a subsequent utility application, the inventor gets a second priority date.
The filing fee for a provisional is 140 dollars for small entities and 70 dollars for micro-entities. Attorney time to assist with drafting and filing can run anywhere from 500 to several thousand dollars.