The aim of the project is to develop a philosophical view on teleological and functional explanations. Teleological explanations are causal explanations of actions, based on the desires and the beliefs of the agent. Functional explanations are causal explanations that give an answer to questions of the form: ``What is the function of E ?" , where E stands for human behaviour or a property of an object that is part of a system. This project includes a descriptive and a normative analysis of both sorts of explanation, in order to become applicable models of explanation.