This book provides a novel perspective on human migration dynamics by examining it through the lenses of complex systems science and philosophy of science. It posits that human migration is not a simple linear process but rather a dynamic phenomenon driven by a multitude of causal factors evolving within complex systems. This book unravels the conceptual and methodological foundations of a complex systems approach to migration, elucidating its ability to explain the intricate causation inherent in migration processes. Additionally, it acknowledges the constraints and challenges faced when adopting this perspective. The research sets out to answer two fundamental questions: (1) Does migration exhibit the dynamics and properties of a complex system? and (2) What are the distinct advantages of employing a complex systems approach for studying migration? The author argues that a complex systems approach provides an integrated framework that comprehensively captures the multilevel structure of migration processes. By doing so, it enables the identification of causation across various scales and elucidates the emergence of complex properties in migration phenomena. Structured into three comprehensive chapters, this book begins with an introduction to the fundamentals of the complex systems approach to migration. The second chapter critically examines the concept of causality within migration science and offers a comprehensive framework for causal inference. The third chapter expands on the notion of multilevel causation and emergence within complex systems of migration. By examining these fundamental issues, this book shows how philosophy can constructively engage with complex systems modeling in order to meet practical scientific objectives and adress contemporary challenges.