This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores the remarkable tenacity of both the word "ghetto" and the multiplicity of practices it came to represent. It examines the ghetto in four separate contexts by using a chronological and transnational approach. First is a place for enclosing the Jewish urban population in Europe, which originated in Venice in 1516 and ended with the fall of the ghetto gates in Rome in 1870. Second is a component of Nazi genocide against the Jews of Europe and the former Soviet Union. Third is a cornerstone of the racial segregation of African Americans in the cities of the United States. And fourth is an implicit and sometimes explicit element in the residential and labor policies established by colonial and post-colonial authorities in South Africa. The book shows how the ghetto emerged from the European segregation of Jews during the early modern era.