One of the issues of Philosophy of Mind is the intentionality of the mind. The topic of this article is the study of the two related aspects of this issue, i.e. the possibility of intentionality and how mind content is determined in the Teleological Theory of Mental Content. According to this theory, the natural evolution of a living organism and the teleological functions based on this determines mental content and one can present a natural and physical explanation of intentionality and (...) mental content with help from that. In this article, after explaining the foundations of this theory, i.e. realism in regards to intentionality, naturalism and the principle of natural evolution of species, we will first address two main versions of this theory, i.e. Dretske’s Indicator Semantics and Millikan Consumer Semantics and then evaluate them. The most important problem of this theory is that it cannot explain the content and meaning of philosophical and logical concepts nor non-existence concepts and therefore, it faces issues concerning the above concepts. (shrink)