The patent system was created to encourage innovation by granting to an inventor an exclusive right to stop others from using her inventions. The system requires an inventor to submit an application to the governmental agency which, in Taiwan, isthe Taiwan Intellectual Property Office. To file a patent application, the applicant might need a specialist who is presumed to acquire the knowledge of paten prosecution and patent law. To become a patent specialist, a person has to pass the patent attor ney bar exam. Among the tested subjects is ―Patent English.‖ The goal of the ―Patent English‖ subject is to examine the language ability of a testtaker to provide patent prosecution services in scussed well. This paper intends to elaborate the content of Patent English. First, the questions tested in the patent attorney bar exam are reviewed to figure out the governmental view regarding Patent English. It is found that the bar exam not only tests English vocabulary used in the patent law but also tests general knowledge about intellectual property issues. Second, this paper analyzes the course of patent prosecution. Three circumstances exist when the English ability is needed. The first circumstance is that a patent attorney might assist foreign applicants to file a patent application. The second circumstance is that a patent attorney might work with foreign patent agents to help Taiwanese clients file a patent applicant in a foreign country, which requires a communication skill in English and a reading skill for analyzing official opinions from foreign patent offices. The third circumstance is that a patent attorney might provide professional opinions about global patent filing strategies to her client, which requires the knowledge or terminologies of patent law. Particularly, she needs to know the American patent law because it influences many countries’ patent laws. This paper concludes that Patent English covers the knowledge of the American pate nt law, business writing skill in English, and essay writing skill in English.