Both the United States government and the terms of an international pact allow you to enjoy the benefits of your discovery for a limited period of time without permitting anyone else to gain profit from it. This is the purpose of a patent, and as of the date of publication, the time period is usually 20 years. Exceptions exist, however.
Article 1, Section 8, of the United States Constitution first recognized the concept of patents. Initially, the Constitution protected the use of an invention for 14 years. In 1861, Congress increased that time frame to 17 years. This duration remained until 1995, when it increased to 20.
World Trade Organization
In 1995, the World Trade Organization was born when more than 150 countries entered into a pact to regulate commerce between nations. The WTO had its roots in GATT, or the General Agreement on Tariffs and Trade, which was signed and ratified by many of these same countries in 1947. GATT and the subsequent founding of the WTO provide the current 20-year duration on all patents issued after June 7, 1995. If your patent issued prior to that date, it expires after 17 years from its date of issue, or 20 years from the date you filed it, whichever is longer.
Your patent might expire earlier than 17 or 20 years under some circumstances. For example, periodic maintenance fees are due to the government to keep your patent “alive.” If you miss one for longer than six months and fail to pay the resulting penalty, your patent will expire prematurely, as of the date of your default. If anyone can prove that your patent is invalid, such as if you used someone else's pre-existing idea, your patent will also expire.
After 17 or 20 years, or if your patent expires earlier for some reason, anyone can sell, use or even copy your invention. Under some isolated circumstances, however, you might be able to prevent this from occurring for another five years. The United States Patent and Trademark Office sometimes grants extensions. If the USPTO takes an inordinate amount of time to approve and issue your patent due to concerns that didn’t bear out, such as if it believed you infringed on another patent but you did not, you can apply to have your term extended. You might also gain additional time if the USPTO denies your patent, but you manage to have that decision overturned on appeal.