This textbook addresses the theoretical backgrounds of migration phenomena as well as the current research fields in migration studies. It systematically presents the classical and contemporary theories of migration sociology, providing an overview of the wide range of different research approaches. Key topics include the classics of migration sociology concerning the stranger, assimilation-oriented cycle models, pluralistic approaches, and migration system theory. Contemporary approaches, such as transnationalism theory and network theory, are also introduced. Significant research fields in migration sociology—such as labor and labor markets, education, integration, flight, irregular migrations, and the feminization of migration—are subsequently examined.