This chapter concerns what we take to be the sin qua non of the aesthetic experience: aesthetic pleasure the immediate hedonic experience elicited by the perception of an object. Many research traditions seek to understand this experience by focusing on either the semantic aspects (associative meanings) or the formal features (colors or shapes) of objects. In contrast, here we suggest that aesthetic pleasure may sometimes derive from another source: the fluency of information processing. In what follows, we begin by defining what we mean by the term “processing fluency.” We then review research showing the hedonic consequences of high processing fluency as expressed in judgments of liking and attractiveness and in psycho-physiological reactions indicative of positive affect. Finally, we conclude with a consideration of the neural basis of fluency and affect. Throughout, we endeavor to show that the concept of processing fluency provides us with a parsimonious explanation for a broad range of aesthetic phenomena: from those originating in the cognitive and social sciences mere exposure, structural relation preferences, prototypicality, and priming-based preferences—to those most often associated with experimental aesthetics—amount of information, symmetry, and contrast and clarity.