This essay draws on cognitive science and cognitive linguistics to illuminate what may be the most important issue in genre theory at present: genre mixture and hybridization. Genres have been very productively treated as cognitive schemas, but so far such treatments have not adequately accounted for critics' descriptions of their encounters with complex works, because they have lacked a model of how schemas are modified, rearranged, and combined. In the past decade, however, Gilles Fauconnier and Mark Turner have worked out just such a model in considerable detail. Conceptual Blending Theory has roots in linguistics, psychology, literary hermeneutics, and brain science. Fauconnier and Turner and others have used Blending Theory to analyze a wide range of thought and meaning, both m undane and highly creative, in the arts, sciences, and everyday life. Taking the example of Joyce's Ulysses, and focusing on the "Circe" episode, I discuss various kinds of genre mixture, showing how surface details as well as structural aspects of the text can be explained in terms of the processes and principles of conceptual blending.