Understanding the trademark law doctrine of foreign equivalents can feel much like an English-language speaker attempting to decipher an article in Welsh: mind-numbing, frustrating, and confounding. This article aspires to be none of those.

This article will begin by showing how the doctrine works in the United States, both in litigation and in proceedings at the United States Patent and Trademark Office (USPTO), with plenty of examples. Then it will dig into the fundamentals of each element, pausing occasionally to wrestle with the doctrine's assumptions, flaws, and inconsistencies. And it will provide a handy checklist of exceptions that prevent the doctrine from being applied.