More than a million migrants and refugees have crossed into Europe during last year sparking a crisis and creating division in an EU under debate. Migration is not only refugee crisis and involves more things. It is important to understand it. The aim of this book is to summarize the migration phenomenon, its causes, factors, and types focusing on the relevant dates to the European Union. The first part of the book analyses the general framework of migration: the stages of the phenomenon, causes, and a revision of the main theories which explain people international movements. The second part focuses on the migration flows in the European Union: colonization movement, evolution and conventions, and agreements. The third part analyses the regulation under EU Treaties and Derived law. Finally, current crisis and the role played by EU institutions were described. This book constitutes an essential reference to understand the migration phenomenon and its implications in the case of EU