1.Introduction: The Liberal International Theory Tradition in Context, Knud Erik Jørgensen.- 2.Liberal IR Theorizing During the Early Twentieth Century: 1900–1939, Lacin Idil Öztig?.- 3. Liberalism and Domestic Politics Approaches in IR, Aukje van Loon.- 4. Republicanism and Liberal International Theory, Kevin Blachford.- 5. Liberal European Peace Theories and Their Critics, Lothar Brock and Hendrik Simon.- 6. Liberal Security Theories, Kamil Zwolski.- 7. When Liberalism Meets the English School, F. Asli Ergul Jorgensen.- 8. Classical Liberalism and IR Theory, Edwin van de Haar.- 9. Conclusion and Perspectives, Knud Erik Jørgensen.