How long do trademarks endure?

A trademark can last indefinitely. There are several things you have to do, however, in order to keep a registered trademark active. Between the fifth and sixth year following registration, you have to file an Affidavit of Use with the Patent and Trademark Office. This is an assertion that the trademark is currently being used in commerce. Ten years after registration, and every ten years thereafter, you have to renew your trademark to keep it active.