Received the first Nevanlinna Prize for outstanding contributions to mathematical aspects of information science. "Pure mathematics enjoys the luxury of studying its constructions, whether finite or infinite, in complete independence of all questions of efficiency." explained Jacob Schwartz, who spoke on Tarjan's work. "By contrast, theoretical computer science must ultimately concern itself with computing engines which operate with limited speed and data storage, and therefore must take efficiency as one of its central concerns. Two closely related activities, algorithm design and algorithm analysis, grow out of this inevitable concern.

For his prescient definition of the “Unique Games” problem, and leading the effort to understand its complexity and its pivotal role in the study of efficient approximation of optimization problems; his work has led to breakthroughs in algorithmic design and approximation hardness, and to new exciting interactions between computational complexity, analysis and geometry.

For transforming our understanding of the computational complexity of fundamental problems in markets, auctions, equilibria, and other economic structures. His work provides both efficient algorithms and limits on what can be performed efficiently in these domains.

For his path-breaking research developing the theory of information complexity, a framework for using information theory to reason about communication protocols. His work has led to direct-sum theorems giving lower bounds on amortized communication, ingenious protocol compression methods, and new interactive communication protocols resilient to noise.