The chapter begins by introducing planning systems in Section 2.2. Then, the BDI agent model is discussed in Section 2.3. This is a logical model of the mental state of the planning agent. Speech act theory is described in Section 2.4, which provides a link between planning and language production. The topic of plan recognition is introduced in Section 2.5, as a prerequisite to understanding of planned dialogue. Meta-level planning, where dialogues are planned that track, modify and support a domain level plan is described in Section 2.6. The combination of planning and plan recognition in producing cooperative responses to a user is described in Section 2.7. A Section on user modelling, Section 2.8, describes the representation, acquisition and maintenance of user models in a dialogue system. In contrast to symbolic planning of dialogue, Section 2.9 describes systems that plan and understand dialogue by ignoring plan structures and using statistical information instead. Section 2.10 describes game theory, which will be used as a quantitative basis for deciding dialogue strategies. Section 2.11 describes approaches to loosely coupled plan decomposition and coordination among agents, and relates these to the problem of dialogue planning. Section 2.12 describes generic or shell systems that use user modelling, which can be programmed with dialogue plan rules to produce a dialogue system. Finally, Section 2.13 describes measures that are used to evaluate dialogue systems.