This edited book focuses primarily on contemporary debates and the critical and postmodern theories to be considered a significant contribution to the field. This book shows that critical international relations theories, which are incomprehensible and challenging, are easy and understandable. The book analyzes the Frankfurt School, constructivism, post-colonialism, feminism, critical geopolitics, political economy, Copenhagen School, Aberystwyth School, Paris School and Ontological security. Critical Theories in International Relations argues that neither identity nor security can be considered a fixed and objective issue, can change according to time and space, and depend on historical and sociological factors. Nothing is given for critical approaches, and they are produced and reproduced in ever-changing conditions that lead to new truths and meanings. These are the results of reflexive and non-linear interactions. In this context, it is made pedagogically understandable to the readers within this framework.