This chapter begins by sketching the standard belief-desire model of action and action-explanation employed by most philosophers, while also noting some variations. Of necessity, given the immense literature on the topic, this is presented at a high level of generality, abstracting over many local disagreements. The model and its variations provide the main set of foils for the scientifically grounded accounts to be discussed in later chapters, which are then briefly previewed. The remaining sections of the chapter go on to explain and quickly motivate three major assumptions that are taken for granted throughout the remainder of the book (and also by many philosophers and almost all cognitive scientists, it should be said): realism, physicalism, and representationalism.