This chapter analyzes patent law in Czechoslovakia in the period from 1945 until the end of communist rule in 1989. In addition to reviewing the legislative development of patent law – the laws on the books – the chapter explains the law in action, which includes the application of the law in practice and the attitudes of Czechoslovak society toward inventive activities and patenting. The chapter aims to achieve three goals. First, it aims to dispel misperceptions that have appeared in some recent scholarship that no developed patent system existed in Czechoslovakia prior to 1989. Second, the chapter contributes to the recent trend in the historiography of the Soviet bloc countries with a showing that patent law development was not uniform across the Soviet bloc, with an explanation that the development did not occur in complete isolation from the West, and with a presentation of the practical everyday effects of the patent system on the people of Czechoslovakia. Third, the chapter presents features of the Czechoslovak patent system that might be of interest to current critics of patent systems in various countries.