This volume contains the papers presented at the3rd International Wo- shoponRandomizationandApproximationTechniquesinComputer Science (RANDOM 99) and the 2nd International Workshop on - proximation Algorithms for Combinatorial Optimization Problems (APPROX 99), which took place concurrently at the University of California, Berkeley, from August 8 11, 1999. RANDOM 99 is concerned with appli- tions of randomness to computational and combinatorial problems, and is the third workshop in the series following Bologna (1997) and Barcelona (1998). APPROX 99 focuses on algorithmic and complexity...