There will be a conference on category theory and its applications in memory of Saunders Mac Lane, April 7 through April 11, 2006, at the University of Chicago. The opening event will be a memorial service, or more accurately a celebration of Mac Lane's life, on the morning of April 7. A number of Mac Lane's students, colleagues, collaborators, and friends will speak during the conference, including Steve Awodey (his last student), Peter Freyd, Andre Joyal, Peter Johnstone, William Lawvere, and Peter May. The mathematical focus will be on recent applications of category theory. The conference will be held in conjunction with the 2006 Unni Namboodiri Lectures, which will be given by John Baez on the afternoons of April 7, 10, and 11, under the general title: ``Higher category theory, higher gauge theory''. As MacLane's book ``Categories for the working mathematician'' emphasized, he was interested both in the internal development of category theory and in its development with a view towards applications in other areas of mathematics. The conference will highlight recent work that introduces new category theory aimed directly at applications in differential geometry (and hence to mathematical physics) and in algebraic topology. As Saunders would have liked, most of the speakers will be young mathematicians actively engaged in just such research. A web page at the address http://www.math.uchicago.edu/~may/MacLane with fuller details will be posted shortly.