Trademark infringement cases in the federal courts turn on the question of "likelihood of confusion": does the defendant's trademark so resemble the plaintiff's that consumers who intend to buy the plaintiff's product may buy the defendant's product by mistake? If the answer is yes, the defendant will likely be permanently enjoined from further use of its trademark.
Likelihood of confusion analysis is also the key issue in opposition and cancellation proceedings in the Trademark Trial and Appeal Board (TTAB), an administrative tribunal of the U.S. Patent and Trademark Office (USPTO), which determines whether the defendant will be entitled to federal registration of its trademark. The TTAB has no authority to enjoin the defendant's use of its mark. But a recent ruling by the Supreme Court suggests that a determination of likely confusion in the TTAB may, under certain circumstances, make a court injunction a virtual certainty.