Mas-Colell es uno de los líderes del movimiento neo-walrasiano. Trabaja en la teoría del Equilibrio General Competitivo. En los años setenta prueba la existencia de un equilibrio competitivo sin utilizar los axiomas de completitud y de la transitividad de las preferencias de los consumidores. Utiliza el cálculo diferencial para explorar las condiciones necesarias para la existencia de equilibrio en una gran variedad de contextos, tanto equilibrios walrasianos como de Nash o de Radner. En 1986 demuestra la existencia de un equilibrio walrasiano en una economía genérica de infinitas dimensiones, lo que ha sido considerado un paso definitivo. 

Es coautor de un manual de Microeconomía (1995) de inmediato éxito y reconocimiento mundial. 

Página web personal de Andreu Mas-Colell en la Universidad Pompeu Fabra.

  Microeconomic Theory
por Andreu Mas-Collel
y otros

The Theory of General Economic Equilibrium
por Andreu Mas-Collel

Noncooperative Approaches to 
the Theory of Perfect Competition
por Andreu Mas-Collel

 Obras de Andreu Mas-Colell

• "Algunas Observaciones sobre la Teoría del Tatonnement de Walras en Economías Productivas", 1974, Anales de Economía
• "An Equilibrium Existence Theorem without Complete or Transitive Preferences", 1974, JMathE.
• "A Note on a Theorem of F. Browder", 1974, Mathematical Programming.
• "An Equilibrium Existence Theorem for a General Model without Ordered Preferences", con D. Gale, 1975, JMathE.
• "A Model of Equilibrium with Differentiated Commodities", 1975, JMathE.
• "On the Continuity of Equilibrium Pricesen Constant-Returns Production Economies", 1975, JMathE.
• "The Demand Theory of the Weak Axiom of Revealed Preference", con Kihlstrom and Sonnenschein, 1976, Econometrica.
• "A Remark on the Smoothing Property of Convex, Complete Preorders", 1976, JMathE
• "Indivisible Commodities and General Equilibrium Theory", 1977, JET.
• "On the Equilibrium Price Set of an Exchange Economy", 1977, JMathE.
• "The Recoverability of Consumer Preferences from Market Demand Behavior", 1977, Econometrica
• "Regular Nonconvex Economies", 1977, Econometrica
• "Some Generic Properties of Aggregate Excess Demand and an Application" con W.M. Neuefeind, 1977, Econometrica
• "A Note on the Core Equivalence Theorem: how many blocking coalitions are there?", 1978, JMathE
• "A Refinement of the Core Equivalence Theorem", 1979, Economics Letters
• "Noncooperative Approaches to the Theory of Perfect Competition: Presentation", 1980, JET
• "Efficiency of Cournot-Nash Equilibriaen Strategic Market Games" con P. Dubey y M. Shubik, 1980.
• "Efficiency Properties of Strategic Market Games: An Axiomatic Approach." P. Dubey y M. Shubik, 1980, JET
• "The Cournotian Foundations of Walrasian Equilibrium Theory: An exposition of recent theory", 1981,en Hildenbrand, editor, Advancesen Economic Theory
• "Walrasian equilibria as Limits of Noncooperative Equilibria: Part I - mixed strategies", 1983, JET
• "On a Theorem by Schmeidler", 1984, JMathE
• "Pareto Optima and Equilibria: the finite-dimensional case", 1985,en Aliprantis et al, editores, Advancesen Equilibrium Theory
• The Theory of General Economic Equilibrium: A differentiable approach, 1985.
• "The Price Equilibrium Existence Problemen Topological Vector Lattices", 1986, Econometrica.
• "Valuation Equilibrium and Pareto Optimum Revisited", 1986, en Hildenbrand and Mas-Colell, editors, Contributions to Mathematical Economics.
• "Notes on Price and Quantity Tatonnement Dynamics", 1986, en Hildenbrand, editor, Models of Economic Dynamics.
• "Engel Curves Leading to the Weak Axiomen the Aggregate" con X. Freixas, 1987, Econometrica
• "An Example of Pareto Optima and Core Allocations far from Agents' Demand Correspondences", con R.M. Anderson, 1988, Econometrica
• "An Equivalence Theorem for a Bargaining Set", 1989, JMathE.
• "Real Indeterminacy con Financial Assets", con J. Geanakoplos, 1989, JET
• "A Geometric Approach to a Class of Equilibrium Existence Theorems", con M. Hirsch and M. Magill, 1990, JMathE
• "A New Approach to the Existence of Equilibriaen Vector Lattices", con S.F. Richard, 1991, JET.
• "Equilibrium Theoryen Infinite Dimensional Spaces", con W.R. Zame, 1991,en Hildenbrand y Sonnenschein, editores, Handbook of Mathematical Economics, Vol. IV.
• "On the Finiteness of the Number of Critical Equilibria: with an application to random selections", con J. Nachbar, 1991, JMathE
• "Infinite-Dimensional Equilibrium Theory: Discussion of Jones", 1992, en Laffont, editor, Advances en Economic Theory
• "Stationary Markov Equilibria" con D. Duffie, J. Geananakoplos, A. McLennan, 1994, Econometrica
• Microeconomic Theory, con M.D. Whinston y J.R.Green, 1995.
• "Existence of Securities Market Equilibrium con a Non-atomic State Space", con W.R. Zame, 1996, JMathE
• "Self-Fulfilling Equilibria: An existence theorem for a general state space", con P.K. Monteiro, 1996, JMathE