The phrase "the Representational Theory of Mind" (RTM) is used in two different but related ways. To understand the difference, one must distinguish two levels at which human beings can be described. The first is personal and belongs to common sense or folk psychology. The second level, in contrast, is subpersonal and scientific. Cognitive scientists and philosophers of cognitive science have offered various characterizations. This chapter begins with the author's own view, based on C.S. Peirce's general theory of representation, and then uses that as a basis of comparison to other views. Cognitive scientists, who conceptualize the mind/brain as, or as substantially like, a computer, take the representation-bearers of mental representations to be computational structures or states. Peirce hypothesized two broad kinds of ground for representation: similarity and causation. Mental representations play multiple roles in cognitive science explanations, which themselves come in many kinds.