International organizations perform activities in areas in which states can no longer operate effectively in isolation, and in which there is a common interest in cooperation within a permanent international framework. This chapter will examine international organizations primarily from a legal perspective. The chapter aims to present a general overview of the law of international organizations. It discusses the legal status, privileges, and immunities of international organizations. The chapter further deals with membership issues, powers, and institutional structures. The chapter also looks at decisions of international organizations: the way in which they are taken and the different types of decisions. The chapter will briefly examine the finances of international organizations. There has been an exponential increase in activities of international organizations over the years. Not all of these activities have been successful, however, and there have been failures and wrongdoings. In recent years, a much-debated issue is the extent to which international organizations and/or their members may be held responsible for such failures and wrongdoings.

This chapter introduces the jus ad bellum: the rules of law determining when states may resort to war or, more broadly, the use of armed force. These rules must be distinguished from the jus in bello: these are the rules of law that apply in armed conflict (known as international humanitarian law). In order to put the current jus ad bellum rules into perspective, the chapter begins by introducing the concept of collective security and demonstrating how this was applied during the League of Nations era. The following sections set out the relevant rules of the UN Charter on the prevention and regulation of recourse to the use of force, with a particular focus on the prohibition on the threat or use of force. The chapter also discusses the collective use of force, meaning the use of force authorized by the Security Council, and the unilateral use of force in self-defense. Finally, the chapter examines whether new exceptions to the prohibition of the use of force are emerging -- in particular, humanitarian intervention and the responsibility to protect.

This chapter introduces the jus ad bellum: the rules of law determining when states may resort to war or, more broadly, the use of armed force. These rules must be distinguished from the jus in bello: these are the rules of law that apply in armed conflict (known as international humanitarian law). In order to put the current jus ad bellum rules into perspective, the chapter begins by introducing the concept of collective security and demonstrating how this was applied during the League of Nations era. The following sections set out the relevant rules of the UN Charter on the prevention and regulation of recourse to the use of force, with a particular focus on the prohibition on the threat or use of force. The chapter also discusses the collective use of force, meaning the use of force authorized by the Security Council, and the unilateral use of force in self-defense. Finally, the chapter examines whether new exceptions to the prohibition of the use of force are emerging -- in particular, humanitarian intervention and the responsibility to protect.