Approximation Algorithms for Scheduling Problems with Exact Delays -- Bidding to the Top: VCG and Equilibria of Position-Based Auctions -- Coping with Interference: From Maximum Coverage to Planning Cellular Networks -- Online Dynamic Programming Speedups -- Covering Many or Few Points with Unit Disks -- On the Minimum Corridor Connection Problem and Other Generalized Geometric Problems -- Online k-Server Routing Problems -- Theoretical Evidence for the Superiority of LRU-2 over LRU for the Paging Problem -- Improved Approximation Bounds for Edge Dominating Set in Dense Graphs -- A Randomized Algorithm for Online Unit Clustering -- On Hierarchical Diameter-Clustering, and the Supplier Problem -- Bin Packing with Rejection Revisited -- On Bin Packing with Conflicts -- Approximate Distance Queries in Disk Graphs -- Network Design with Edge-Connectivity and Degree Constraints -- Approximating Maximum Cut with Limited Unbalance -- Worst Case Analysis of Max-Regret, Greedy and Other Heuristics for Multidimensional Assignment and Traveling Salesman Problems -- Improved Online Hypercube Packing -- Competitive Online Multicommodity Routing -- The k-Allocation Problem and Its Variants -- An Experimental Study of the Misdirection Algorithm for Combinatorial Auctions -- Reversal Distance for Strings with Duplicates: Linear Time Approximation Using Hitting Set -- Approximating the Unweighted k-Set Cover Problem: Greedy Meets Local Search -- Approximation Algorithms for Multi-criteria Traveling Salesman Problems -- The Survival of the Weakest in Networks -- Online Distributed Object Migration.

This book constitutes the thoroughly refereed post proceedings of the 4th International Workshop on Approximation and Online Algorithms, WAOA 2006, held in Zurich, Switzerland in September 2006 as part of the ALGO 2006 conference event. The 26 revised full papers presented were carefully reviewed and selected from 62 submissions. Topics addressed by the workshop are algorithmic game theory, approximation classes, coloring and partitioning, competitive analysis, computational finance, cuts and connectivity, geometric problems, inapproximability results, mechanism design, network design, packing and covering, paradigms, randomization techniques, real-world applications, and scheduling problems.