 Kirschner is a pioneer in using mathematical approaches to learn about central biological questions.For example, a model of the Wnt pathway he developed in collaboration with the late Reinhart Heinrich showed that new properties and constraints emerge when the individual biochemical steps are combined into a complete pathway.A talk he gave on mathematics and the future of medicine at a retreat for Department Chairs at Harvard Medical School in 2003 inspired the Dean, Joseph B. Martin, to found a new Department, the Department of Systems Biology, with Kirschner as founding chair.