This brief note is not legal advice and is for educational purposes only.
When you file a patent application you get a “priority date”. This is generally the earliest date that you filed and it establishes a date for “prior art” references. That is, during the patent examination process (called patent prosecution), references after the priority date cannot be used in the examination to reject your application. Thus, the importance of a priority date.
During prosecution you may have amended the claims to overcome some cited art and may have narrowed the scope of what was claimed. Often this is done to get the inventor an issued patent as soon as possible, for such purposes as fundraising, licensing, filing a lawsuit against an infringer, etc.
During prosecution you may also have received a “restriction” which basically says the examiner believed there was more than one invention in the application, and you had to pick which one to initially pursue. The others can be pursued if an application is co-pending in what are called “divisional” applications (think examiner divided your application).
Before the patent issues you have the option to file what is called a “continuation” application which is based on the originally filed application and most importantly gets its priority date. (There is also a continuation-in-part (CIP) – which can introduce new matter – it gets complicated.)
So why would you want to file a continuation? There are several reasons.