The mathematical research of Marston Morse, extending over most of the past half-century, has exercised a deep and ever widening influence. In the tradition of great mathematicians, he initiated and extensively developed new and bold theories, affecting the main currents of modern mathematics. His investigations of critical points and his theory of the calculus of variations in the large involved a combination of analysis and topology in the spirit of Poincaré. These parts of Morse’s research are basic to some of the major recent developments in differential and combinatorial topology. Of all the mathematical areas influenced by the broad spectrum...