The architecture of a multi-agent system can naturally be viewed as a computational organisation. For this reason, we believe organisational abstractions should play a central role in the analysis and design of such systems. To this end, the concepts of agent roles and role models are increasingly being used to specify and design multi-agent systems. However, this is not the full picture. In this paper we introduce three additional organisational concepts-organisational rules, organisational structures, and organisational patterns-that we believe are necessary for the complete specification of computational organisations.We view the introduction of these concepts as a step towards a comprehensive methodology for agent-oriented systems.