The advantages of the agent-based approach are still not widely recognized outside the agent research community. In this paper we use patterns as a way of motivating the use of agents. Patterns have proven to be an effective means for communicating design knowledge, describing not only solutions, but also documenting the context and motivation for applying these solutions. The agent community has already started to use patterns for describing best practices of agent design. However, these patterns tend to pre-suppose that the decision to follow an agent approach has already been made. Yet, as this author has experienced on many occasions, that is usually far from a given. There is a need for guidelines that summarize the key benefits of the agent approach, and serve as a context for more specific agent patterns. Our response to this need is a pattern language - a set of patterns that build on each other - that introduces the concepts of agent society, roles, common vocabulary, delegation, and mediation. We also argue that authors of agent patterns should aim to organize their patterns in the form of pattern languages, and present a template for pattern languages for agents.