As an introduction for undergraduate students of political science or a reference work for advanced semesters, this volume presents central concepts and theories and systematically connects them with the key phenomena of international relations. The first part covers the history of international relations and its global trends from the Congress of Vienna to the Arab Spring. The second part deals with the main theories of international relations and explains their fundamental assumptions and explanatory claims. Finally, the third part introduces the most important current research fields and discusses central issues from the perspective of international relations theories. Extensive supplementary material available online enhances the presentation and offers opportunities for further exploration.