This chapter begins with a discussion of the philosophical precedents that gave rise to the development of functionalism. On first thought, functionalism may seem to be a version of physicalism. Unlike the identity theory, functionalism would not be a version of type physicalism, but it’s natural to see it as a version of token physicalism – and indeed, that’s how many functionalists cast themselves. Two further advantages are often thought to accrue to functionalism. First, it fits nicely with our practices of attributing mental states to others, what is sometimes called the problem of other minds. Functionalism’s second advantage stems from its commitment to multiple realizability. The chapter also considers different thought experiments that are commonly raised in objection to functionalism. The upshot of the absent qualia objection is that functionalism attributes mentality to entities that it shouldn’t, i.e., entities that don’t have qualia.