The world has changed in several ways after the end of the cold war; the greatest current threats to international peace and security are no longer traditional interstate wars. International terrorism, gross violations of humanitarian law and human rights, failed states and internal wars, widespread use of landmines, fear of the use of weapons of mass-destruction and cyberspace attacks have seriously challenged the traditional concepts in international law and security discourse. The shocking terrorist acts of September 11 dramatically accelerated this development. The UN has struggled to meet these challenges in various ways and with changing success. A number of peacekeeping operations and humanitarian interventions have been conducted, international criminal law has had a breakthrough during the 1990s, and a right to self-defence against large-scale international terrorism evolved following September 11. The book analyzes these recent trends and phenomena according to the rules on international peace and security and the use of force. The writers are academics working at Swedish universities, the Swedish Military Academy and the Swedish Ministry for Foreign Affairs. The book is mainly intended for scholars and advanced students in public international law and humanitarian law, and for further education at military academies and defence colleges. It is also suggested for anyone interested in recent developments in these fields.