This chapter addresses how agent organisations can improve and accelerate coordination processes in open environments. A state-of-art of recent proposals for describing agent organisations is given, relating the different methodologies and formal approaches for defining agent organisations in an explicit way. As example, four different proposals developed within the COST action IC0801 are detailed: (i) the MOISE organisation Model, which provides structural, functional and normative specifications of an organisation, and it is integrated in an Organisation Management infrastructure; (ii) the Virtual Organisation Model, which describes the structural, functional, dynamical, environmental and normative dimensions of an organisation, and it is complemented by the Virtual Organisation Formalization; (iii) the Agent-Oriented Modelling for sociotechnical systems, which are organisations consisting of human and man-made agents; and (iv) the AAOL agent architecture, in which groups of autonomous agents are organized in Localities. This chapter proposes a global comparison of different existing organisational models with the four detailed models in terms of the different description dimensions they propose.