The doctrine of equivalents is arguably one of the most important aspects of patent law. The protection a patent confers is meaningless if its scope is determined to be so narrow that trivial changes to a device bring it out of the bounds of the patent. One of the greatest challenges courts and legislatures therefore face in patent law is to create rules for determining patent scope that maintain the protection a patent is meant to confer while still keeping the patent monopoly within reasonable bounds. Despite the general unity in patent laws among developed countries, the difficulty of this task has led to different results in different jurisdictions. Many jurisdictions have chosen to determine patent scope under a doctrine of equivalents, while others have maintained the position that adequate scope can be found within the meaning of a patent’s claim. Even jurisdictions which agree that a doctrine of equivalents should apply differ significantly in its application. This Article provides an examination of four patent jurisdictions—the United States, the United Kingdom, Germany, and Japan—and their separate answers to the question of patent scope. This Article does not purport to decide which jurisdiction has the right solution, but merely points out that different solutions can be and have been found for the question of equivalents. Although a traditional case of patent infringement under the doctrine of equivalents may find protection under all four jurisdictions, the laws of these countries start to diverge on questions regarding after-arising technology, the essential elements of a patent claim, and equivalents that clearly fall outside the language of a claim. One cannot answer the question, “Does anybody have it right?” without first considering these issues.
