Celebrating the twenty-fifth anniversary of the Oxford University Mathematical Economics Seminar, this collection of papers discusses topics in theory, policy, and theory for policy, and illustrates ways in which mathematical modeling can provide insights into economic theory. Contributors include Robert Solow, Peter Hammond, Joseph Stiglitz, Andrew Weiss, Joseph Farrell, David Ulph, N.H. Stern, Avinash Dixit, John Kay, and Martin Feldstein.