Dear category theorist: This is a call for participation in a special session on Mathematical Applications of Category Theory which will take place at the Winter Meeting of the Canadian Mathematical Society, to be held December 8-10, 2007, in London, Ontario. All information (as currently available) may be found at http://www.cms.math.ca/Events/winter07/ The following people have already accepted invitations to speak in the session: Bernard Badzioch, University at Buffalo Michael Barr, McGill University John Bell, University of Western Ontario Marta Bunge, McGill University Jonathon Funk, University of the West Indies Ernie Manes, University of Massachusetts Susan Niefield, Union College Robert Pare, Dalhousie University Dorette Pronk, Dalhousie University Bob Rosebrugh, Mount Allison University Myles Tierney, University of Quebec at Montreal Richard Wood, Dalhousie University We have space for a few additional speakers. All talks in the session will be 20-minute presentations, with an additional 10 minutes reserved for discussion and transition between sessions. If you are interested in giving a talk at the session, please contact Walter Tholen at tholen@mathstat.yorku.ca by May 15, 2007. We hope to see you at the session. Bill Lawvere and Walter Tholen (Organizers)