From time immemorial human beings migrated for many reasons. Theorists offered various explanations why they move from the place of their origin to another destination. Over the past centuries, forms, dynamics, routes and volumes of migration have changed dramatically. No single theory can provide a comprehensive explanation for the current migration trend. Ernest Ravenstein developed his Laws of Migration in 1889 and concluded that migration was governed by a push-pull process. Many theorists have followed in Ravenstein's footsteps, and the dominant theories in contemporary scholarship are more or less variations of his conclusions. However, most theories are region or country specific. This collection offers simplified explanations of dominant theories from different perspectives, and some experiences from Bangladesh. This is an essential piece of work for geographers, researchers and academics from any discipline in social sciences.