This paper explores the relationship between Jews and communism in the twentieth century through a case study of the Jewish membership of the Communist Party of Great Britain (CPGB). It explains in particular why large numbers of Jews were attracted to the CPGB. The dynamics of integration into British society of second-generation Anglo-Jewry provides an answer and offers an insight into the issues of Jewish identity and its relationship with extreme left-wing politics. The study of the personal reflects wider changes in the historiography of communism as the end of the communist bloc has led to new avenues of research not least due to the opening of previously closed archives. Indeed, the sources used here have only recently been made available following the demise of the CPGB. This article concentrates on the one of the most important parts of this archive: the biographical collection, a unique source providing an unparalleled opportunity to examine the lives of party members. This article represents one of the first to be based on this material, and with additional supporting research it also represents probably the largest and most detailed biographical study of Anglo-Jewry to date.