From an agent architecture perspective and analysing the reasoning capabilities of agents with respect to organisations, different cases may be considered: agents may or may not have an explicit representation of the organisation, and they may or may not be able to reason about it. Organisational reasoning agents have the capability to represent the organisation and are able about reason on it. In this chapter, we will discuss the main features of this kind of agents and which are the fundamental mechanisms for reasoning about organisations. We will also describe some approaches proposed in the literature related to how agents can take decisions on their participation in an organisation.