Most readers probably take it as self-evident that literature is inseparable from emotion. Poems memorialize love and grief; stories elaborate on the rage of battle, the shame of defeat, or the guilt of sin. Readers pass through versions of these feelings while perusing a book or watching a play. They also experience respect and awe, flip pages or inch forward in their seats due to suspense, or relax into a delighted experience of beauty at a phrase or scene. After long neglect, in recent decades, emotion—or, more generally, affect—has become a major concern in literary study, as well as philosophy, psychology, and elsewhere. It is possible to organize such work into two broad orientations, commonly called “affect theory” (alternatively, “affective poststructuralism”) and “affective science.” Writers in affect theory draw on a range of psychological, social, linguistic, and other theories, most often in the service of political analysis. The psychological principles of affect theory have tended to derive from the tradition of psychoanalysis, often through its radical revision or critique by such theorists as Jacques Lacan and Gilles Deleuze. Affect theorists have also drawn extensively, sometimes more centrally, on a range of theorists outside of psychology, principally poststructuralists, such as Michel Foucault and Jacques Derrida. In contrast, affective science has its roots in cognitive science and to a lesser extent social psychology. It comprises a set of competing theories of emotion, including dimensional versus systemic and appraisal versus perceptual-associative accounts. Dimensional accounts see emotions as specified only by general variables (such as attraction versus aversion). Systemic accounts treat emotions as the result of distinct pre-dedicated, biological systems (e.g., for disgust or fear). Appraisal accounts treat emotion as the result of a person’s assessments of how events or circumstances impact his or her achievement of important goals. Perceptual-associative accounts construe emotion as a more mechanical process that is affected by assessments only indirectly. Whatever its explanatory architecture, an affective science account is likely to include a careful analysis of emotion episodes, breaking them down into eliciting conditions, action readiness, expressive or communicative outcomes, phenomenological tone, and other components. Beyond treating different theories of emotion, an account of literary affect needs to consider the various possible locations of emotion in literature. These begin with the real people involved—authors and readers. But they extend to implied authors and implied readers as well as wholly fictional persons, such as narrators and characters. Emotion bears also on scenes and sequences—both the sequence of events as they actually occur in the story and the sequence of events as they are presented in the plot (which may, for example, reveal the outcome of events before revealing their causes). Sometimes, a given narrative level has its own characteristic emotions or affective concerns—such as suspense in the case of plot (suspense is in part a function of when story information is provided). At other times, a given level will merely affect the ways the emotions of other levels are modulated (as when some stylistic features, not funny in themselves, contribute to comic effect). By the usual scientific criteria, affective science is more logically rigorous and empirically better supported. But affect theory has its own value—particularly in challenging the ideological assumptions that often underlie social scientific research, including some of that undertaken in affective science. In short, each group has something to learn from the other.