I have been selling my product for five years can I get a patent?

The patent system is an exchange between the Federal Government and the inventor.  In exchange for publicly disclosing his or her invention in a patent, the U.S. provides the inventor with (at current) a 20 year pseudo monopoly on the invention.  The patent grant provides the right to keep others, for example, from making, selling, using, the invention.  If the invention is already in the public domain, there is no incentive for the Patent Office and the Federal Government to grant these patent rights.

However, the U.S. provides a one year grace period to inventors. If an inventor publicly discloses his or her invention today, the inventor has one year to file a patent application.  In some foreign countries, including in European countries and the European Union, there is no grace period.  Canada utilizes a modified grace period of six months.

There are exceptions to the public disclosure, including if the disclosure was for experimental purposes or if the disclosure was not sufficient for members of the public to determine what constitutes the patentable invention.

Thus if it is possible for a third party to easily copy your invention, it is a good idea to seek patent protection before the grace period runs out.