In this critical evaluation of the evolution of the field of international relations over time, Sullivan reflects on how the interaction of real world events, academic trends and methodological debates has resulted in shifts in focus while certain topics or questions remain persistent. Combining synopses of both intellectual developments and empirical research, this study should be of interest to students seeking an overview of developments in international relations theory and research. The text is a synthetic historiography of international relations theory at the beginning of the 21st century, a critical analysis of the continuing diversity and complexity of enduring themes through a sustained focus on the analysis of the empirical evidence accumulated by social scientists. Special attention is given to key historical changes in theoretical approaches since the mid-20th century with full recognition of the contestation over state-based theory and the changing fortunes of contemporary approaches. The book suggests that viable theories must transcend passing intellectual fashions, and attempts to bring together theory and practice while demonstrating the difficulty of assessing competing theories. It addresses multiple strands of thought and assumes that their development cannot be understood in isolation from each other.