This chapter reviews the theoretical underpinnings of the alien conspiracy and ethnic succession theories as explanations for the emergence and continuation of organized crime in American society. It first considers the arguments of the alien conspiracy theory, as well as the cultural deviance theory upon which it is based, before discussing the claims of the social disorganization theory as the basis of the ethnic succession theory. The chapter also examines the theories of human ecology, cultural transmission, and differential social organization, along with delinquency theories and their relation to organized crime, with particular emphasis on recruitment issues. Finally, the chapter looks at the relationship between Gerald Suttles's conceptualization of the defended neighborhood and racket subcultures.