The literature on migration keeps evolving with the ever-changing trends in migration owing to different global and local factors. Therefore, a single theory on migration, be it internal or international, cannot be ascertained. Each migration theory focuses on a given form of mobility and its theoretical basis. This chapter tries to condense and summarize the most widely discussed theories on migration in the literature, and tries to classify the different models and theories into different heads for a clearer perspective on such issues. While different theories on migration in literature reflect on different aspects of migration, they do supplement and complement each other in understanding the picture as a whole.