The contents of this volume comprise the proceedings of the conference, "Equilibrium theory and applications." Some of the recent developments in general equilibrium theory in the perspective of actual and potential applications are presented. The conference was organized in honor of Jacques Drèze on the occasion of his sixtieth birthday. Held at C.O.R.E., it was also the unanimous recognition, stressed by Gérard Debreu in his Address, of his role as "the architect and builder" of the Center for Operations Research and Econometrics. An introductory address by Gérard Debreu comprises Part 1 of the volume. The rest of the volume is divided into four parts spanning the scope of the conference. Part 2 is on incomplete markets, increasing returns, and information, Part 3 on equilibrium and dynamices, Part 4 on employment, imperfect competition, and macroeconomics, and Part 5 on applied general equilibrium models.