Interactions are a core part of all multi-agent systems. They occur because of the inter-dependencies that inevitably exist between the agents and they manifest themselves in many different forms–including cooperation, coordination, and collaboration. However, perhaps the most fundamental and powerful mechanism for managing these inter-agent dependencies at run-time is negotiation–the process by which a group of agents communicate with one to try and come to a mutually acceptable agreement on some matter. Negotiation underpins attempts to cooperate and coordinate (both between artificial and human agents) and is required both when the agents are self interested and when they are cooperative. It is so central precisely because the agents are autonomous. For an agent to influence an acquaintance, the acquaintance needs to be convinced that it should act in a particular way. The means of achieving this state are to make proposals, trade options, offer concessions, and (hopefully) come to a mutually acceptable agreement. In short, to negotiate.