Long before the emergence of the World Wide Web, librarians had a long tradition of collecting and classifying physical materials. Influenced by these activities, information literacy instruction has defined and taught sources as objects of similar content and/or format. Because of their ability to organize information for easy retrieval, such definitions are helpful from a practical standpoint. Unfortunately, they do little to account for a source's role as a communicative act shared within and between communities. To expand our definition we must look to Genre Theory. Genre Theory examines how groups develop language—genres--to respond to recurrent, rhetorical situations. Seen as purposeful choices to aid in the completion of specific tasks, it is possible to comprehend the meaning of certain forms and why they are chosen. The theory also illustrates how these choices serve ideological purposes by establishing expectations in the readers of the genre. Implications for teaching a generic theory of sources are also discussed.