Part I. Development of the Contemporary Jus ad Bellum in International Law: 1. Introduction; 2. From just war to the great war; 3. From the regulation of war to the prohibition on the use of force; Part II. Scope and Content of the Contemporary Jus ad bellum: 4. The prohibition on the use or threat of force; 5. The use of force in the un collective security system: maintenance and restoration of international peace and security through collective measures; 6. The right of self-defence: essence, function and legal foundation, requirements for exercise, scope and modalities of application; Part III. Controversies and Contested Justifications for the Use of Force: 7. Humanitarian intervention and the responsibility to protect; 8. The use of force and the rescue and evacuation of nationals; 9. Armed reprisals and the law on the use of force; 10. The use of force and weapons of mass destruction; 11. New technologies of warfare and the law on the use of force; Part IV. The Use of Force within the Wider Legal Landscape: 12. The use of force as an attribute of state sovereignty; 13. The use of force in the international commons; 14. The relationship of the law on the use of force with the law of armed conflict and human rights law; 15. International responsibility for the unlawful use of force: states, organizations, armed groups and individuals; Part V. Concluding Remarks: 16. Conclusions.