This volume contains the papers presented at the 6th International Workshop on Randomization and Approximation Techniques in Computer Science (RAN- DOM 2002), which took place at Harvard University, Cambridge, Massachusetts, from September 13-15, 2002. RANDOM 2002 was concerned with applications of randomness to computational and combinatorial problems, and was the sixth workshop in the series following Bologna, Barcelona, Berkeley, Geneva, and B- keley again. The volume contains 21 contributed papers, selected by the program c- mittee from 48 submissions received in response to the call for papers. We thank all of the authors who submitted papers, our invited speakers, the members of the program committee: Dimitris Achlioptas, Microsoft Research Martin Dyer, U. of Leeds Uriel Feige, Weizmann Institute Russell Impagliazzo, UC San Diego Sampath Kannan, U. of Pennsylvania David Karger, MIT Nati Linial, Hebrew U. Rafail Ostrovsky, Telcordia Technologies Paul Spirakis, U. of Patras and CTI Angelika Steger, TU Munich R¿udiger Urbanke, Swiss Federal Inst. of Tech. Salil Vadhan, Harvard U., chair, and the external reviewers: N. Alon, R. Alur, A. Ambainis, T. Batu, J. Feig- baum, S. Gerke, Y. Gertner, A. Goerdt, L. Goldberg, J. Hastad, C. Iliopoulos, Y. Ishai, V. Kabanets, S. Khot, L. Kirousis, S. Kontogiannis, M. Krivelevich, M. Mavronicolas, A. McGregor, F. McSherry, D. van Melkebeek, M. Molloy, E. Mossel, S. Nikoletseas, R. Raz, D. Ron, P. Tetali, L. Trevisan, E. Vigoda, J. Watrous, and P. Winkler.

Counting Distinct Elements in a Data Stream.- On Testing Convexity and Submodularity.- ?-Regular Languages Are Testable with a Constant Number of Queries.- Optimal Lower Bounds for 2-Query Locally Decodable Linear Codes.- Counting and Sampling H-Colourings.- Rapidly Mixing Markov Chains for Dismantleable Constraint Graphs.- On the 2-Colorability of Random Hypergraphs.- Percolation on Finite Cayley Graphs.- Computing Graph Properties by Randomized Subcube Partitions.- Bisection of Random Cubic Graphs.- Small k-Dominating Sets of Regular Graphs.- Finding Sparse Induced Subgraphs of Semirandom Graphs.- Mixing in Time and Space for Lattice Spin Systems: A Combinatorial View.- Quantum Walks on the Hypercube.- Randomness-Optimal Characterization of Two NP Proof Systems.- A Probabilistic-Time Hierarchy Theorem for "Slightly Non-uniform" Algorithms.- Derandomization That Is Rarely Wrong from Short Advice That Is Typically Good.- Is Constraint Satisfaction Over Two Variables Always Easy?.- Dimensionality Reductions That Preserve Volumes and Distance to Affine Spaces, and Their Algorithmic Applications.- On the Eigenvalue Power Law.- Classifying Special Interest Groups in Web Graphs.