These notes have their origin in a course given at Princeton University in the fall of 1968; I am most grateful to Princeton for providing the opportunity to give such a course and to those institutions which provided support during the preparation of these notes: Princeto n , the University of Notre Dame, The Institute for Advanced Study, the Alfred P. Sloan Foundation and NSF Grant
GP-9590. The course itself was presaged by a lecture at the Michigan State Conference on the Topology of Manifolds [Stasheff]. The present arrangement of topics owes much to a short course given at Boston College in the fall of 1969. Finally, my deep gratitude to Mrs. Ann Gosling of Princeton University
and Miss Evelyn Laur~nt of The Institute of Advanced Study for their fine preparation of preliminary and final typescripts of these notes.