Traditional theories of categorization in which categories are assumed to be grounded in perceptual similarity or theories ignore an important, and very different, basis of conceptual structure: the discrete emotion that a stimulus elicits in the perceiver. We argue that emotional responses are detectable dimensions of stimuli that can be attended to and used as a basis of equating them organizing them into categories. This article discusses the nature of, and theoretically and empirically reasonable constraints on, emotional response categories, and explores the conditions under which they are used. A series of experiments in which participanats sort triads of concepts that share both emotional and non-emotional similarities indicate clearly that people are more likely to use emotional response categories when they are experiencing strong emotional states themselves. Multidimensional scaling of similarity judgments of emotional and non-emotional perceivers support a proposed selective attention mechanism of these effects. Participants induced to feel happy or sad emotional states weighted emotional response-related dimensions of stimuli more heavily than people in relatively neutral states. The triad and multidimensional scaling data, along with a number of functional considerations, suggest that emotional response categorization is not only tenable, but necessary for a complete account of conceptual coherence.