Michael Green has made outstanding contributions to quantum field theory, especially the theory of superstrings. Michael’s early work was largely on duality in S-matrix theory. He was the first to prove an important result on the dual model — the cancellation of the leading divergences between boson and fermion loops. He has made significant contributions to the theory of phase transitions, but is best known for his work, much of it in collaboration with John Schwarz, on superstring theory, including the first covariant formulation of the theory. The most important results are the proofs in 1984 and 1985 of anomaly cancellation for SO (32) and E8 x E8 superstring theories and of infinity cancellation in the SO (32) case. These definitive papers initiated the explosive growth of superstring theory, now one of the most active and exciting areas of fundamental theoretical physics.