In this chapter, we discuss the concepts of agent organization, organizational model, and review some existing organizational models. Before the review, we discuss how to classify the diverse aspects of agent organizations currently captured by organizational models. These aspects are named "modelling dimensions". We show that there are at least four basic dimensions: the structural dimension mainly composed of roles and groups, the interactive dimension characterized by dialogical interaction structures, the functional dimension formed by goal/task decomposition, and the normative dimension in which we find the concepts of norms, rights, rules, and so forth. Apart from the basic dimensions, we also identify four other complementary dimensions: environment, evaluation, evolution, and ontology. These are related to the aspects of situatedeness, measurement, adaptation, and domain specific semantics of agent organizations. Finally, we compare the organizational models reviewed and describe how the idea of modelling dimension can help in finding correspondences between organizational models.