This chapter presents a brief survey of methods used in order to arrive at a genetic classification of African languages, and more specifically of multilateral or mass comparisons, as well as the comparative method. The study of dialect variation is another approach that has led to new insights into genetic diversification and the spreading of linguistic innovations. The chapter addresses language ecology, and more specifically the degree of genetic diversity in different parts of the continent, as well as the issue of accretion and spread zones in Africa. It provides some suggestions for future comparative studies of African language families. Much of the subsequent historical-comparative work on African languages during the 19th century and the early 20th century became marred with racist connotations, also mixing up genetic and typological classifications. Some scholars also prefer to treat some of the languages listed in Joseph H. Greenberg as members of the four major African language families as linguistic isolates.