The English word “imagination” is the standard translation of the Greek phantasia. This chapter examines two contrasting ways in which the term phantasia is used in ancient aesthetics. Phantasia in the sense of “visualization” is common in a variety of texts discussing poetry, oratory, historiography, and painting from the first century AD onward, including Longinus, On Sublimity, although the origins of the concept go back to Homer. This sense of phantasia is often connected with enargeia, “vividness.” The use of phantasia to refer to a kind of imagination which goes beyond everyday experience is much less common, but can be found in some Neoplatonist texts.