This chapter explores some implications of the theories for the computational theory of mind (CTM). After highlighting some general features of implementation, it reviews the theories on offer and how they address the challenge of pancomputationalism, namely, the thesis that every physical system computes. The chapter argues that satisfying minimal desiderata for theories of implementation – to avoid the most damaging form of pancomputationalism – sharply limits the degree to which psychology is autonomous from neuroscience. Strong versions of CTM maintain that the nature of mental states is wholly computational. Weak versions of CTM maintain that at least some cognitive phenomena are explained by mental computations, although there may be more to the nature of mental states than computational properties. A theory of implementation specifies the conditions a physical system must satisfy in order to carry out a computation.