In this paper, I present a new "taxonomy of functions' that reviews the different theories on functional explanations which can be found in the current debate in philosophy of biology. I begin by presenting a critical survey of the classical ways of interpreting the notion of function (the "causal-role" and the "evolutionary" approaches) under the light of the current theoretical proposals. I then analyze the major novelty in the philosophical discussion on functions: the Organizational Approach. According to organizational theories, a function is a disposition of a particular current biological trait that has explanatory relevance with regard to the presence of the function-bearing trait. The organizational account claims that a functional effect can be understood as a "condition of existence" of that very trait (without appealing to evolutionary history) to the extent that it is a necessary condition for the process of biological self-maintenance of the organism.