What is reissue?
Patent law states "On taking up an application for examination or a patent in a reexamination proceeding, the examiner shall make a thorough study thereof and shall make a thorough investigation of the available prior art relating to the subject matter of the claimed invention." This means that prior art could disqualify your application for a patent.The Poor Man's Patent is a Myth
One of the undying myths of Patent World is that there is such a thing as a Poor Man's Patent. If you've never heard of it, the poor man's patent involves writing out a description of your invention and mailing that description to yourself. The transmission of this description through the mail and the cancelling of the postage by the Post Office is supposed to establish a date of invention for you. That way if someone steals your invention or comes along and invents it independently, you have "proof" that you invented it first. The proof is in the sealed envelop and the date the postage was cancelled.How do I know if my idea is patentable?
First, check to see if your idea qualifies. Second, learn the basics of the patenting process. Next, do a search for of all previous public disclosures that concern your invention. These public disclosures are called prior art. A registered patent attorney or agent can be hired to do a patentability search for prior art, and a big part of that is searching for U.S. and foreign patents that compete with your invention. After an application is filed, the USPTO will conduct their own patentability search as part of the official examination process.Provisional Application
If you have a patentable invention, filing a provisional patent application can provide temporary protection of your intellectual property rights while you develop your idea further or seek funding. Provisional applications have a lower fee than non-provisional applications -- and you don't have to make formal claims or provide the same level of detail about your invention. Additionally, provisional applicants don't have to wait for the USPTO to examine the contents of the application. Your provisional application is valid 12 months from the date you file it -- and you can use the phrase "patent pending" in connection with your invention during that time.What cannot be patented?
Laws of nature, Physical phenomena, Abstract ideas, Inventions which are considered not useful or possible by the USPTO for example perpetual motion machines; or offensive to public morality.