This chapter discusses the study of global migration, it is necessary to distinguish between different types of migration. It describes some of the major theories that explain why migration occurs. The United Nations Statistics Division (UNSD) and the International Organization for Migration (IOM) represent valuable sources for migration statistics. The chapter examines the number of theories that offer an understanding of the migration process, with a focus on the movement of people because of economic reasons. It highlights the work by one of the earliest theorists of migration, Ernest George Ravenstein, and then we integrate more contemporary scholarly work on recent understandings of global migration processes. The chapter focuses on processes related to migration, including assimilation, ethnicity, segregation, multiculturalism and transnational migration. It explores the nexus between migration and sexuality, focusing in particular on the policy environment for lesbian, gay, bisexual and transgendered (LGBT) individuals.