MRST 2001, the 23rd of a series of meetings in theoretical high energy physics that normally rotate between McGill University, the University of Toronto, the University of Rochester and Syracuse University, honours the memory of Roger Migneron, a frequent participant in past MRST meetings and a strong contributor to elementary particle physics in Canada. Two special sessions present exciting advances in theoretical high energy physics by several outstanding physicists. Topics include: gravity/geometry; B-physics; quarks, gluons and mesons; field theory; and branes, strings and things.