This book delves deep into the mechanics of the phenomenon of immigration. It looks at all the different categories of populations that move out of their homeland for a variety of reasons –- refugees and asylum seekers, displaced populations, and economic immigrants. The book carries out a deconstruction of human immigration at a molecular level, approaching from a wider multitude of epistemological positions, examining through different lenses, including the evolutionary, spiritual, psychological, economic, and political perspectives. Finally, it endeavours to develop a unified theory of immigration with short- and long-term real-world implications of immigration at an expansive global and far-reaching temporal scale. The volume will be useful for students and researchers of migration, diaspora, psychology, sociology, mental health, public health, and public policy.