"This is the first of four volumes of the collected papers of Leonid Hurwicz, one of the premier mathematical economists of the 20th century whose research spanned over 6 decades. A co-recipient of the 200 7NobelMemorial Prize (with Eric Maskin and Roger Myerson) for "laying the foundations of mechanism design" - the design of decentralized institutions to bring about socially desirable outcomes when markets may fail to do so - Leo's contribution to economics has been far wider, ranging from econometrics, programming, and decision theory to microeconomic theory. It has been said that his classic 1971 paper with Hirofumi Uzawa on the integrability of demand functions alone qualifed him for the Nobel"--