Invited Presentations -- On Salesmen, Repairmen, Spiders, and Other Traveling Agents -- Computing a Diameter-Constrained Minimum Spanning Tree in Parallel -- Algorithms for a Simple Point Placement Problem -- Duality in ATM Layout Problems -- Regular Presentations -- The Independence Number of Random Interval Graphs -- Online Strategies for Backups -- Towards the Notion of Stability of Approximation for Hard Optimization Tasks and the Traveling Salesman Problem -- Semantical Counting Circuits -- The Hardness of Placing Street Names in a Manhattan Type Map -- Labeling Downtown -- The Online Dial-a-Ride Problem under Reasonable Load -- The Online-TSP against Fair Adversaries -- QuickHeapsort, an Efficient Mix of Classical Sorting Algorithms -- Triangulations without Minimum-Weight Drawing -- Faster Exact Solutions for Max2Sat -- Dynamically Maintaining the Widest k-Dense Corridor -- Reconstruction of Discrete Sets from Three or More X-Rays -- Modified Binary Searching for Static Tables -- An Efficient Algorithm for the Approximate Median Selection Problem -- Extending the Implicit Computational Complexity Approach to the Sub-elementary Time-Space Classes -- Group Updates for Bed-Black Trees -- Approximating SVP ? to within Almost-Polynomial Factors Is NP-Hard -- Convergence Analysis of Simulated Annealing-Based Algorithms Solving Flow Shop Scheduling Problems -- On the Lovász Number of Certain Circulant Graphs -- Speeding Up Pattern Matching by Text Compression.

The papers in this volume were presented at the Fourth Italian Conference on Algorithms and Complexity (CIAC 2000). The conference took place on March 1-3, 2000, in Rome (Italy), at the conference center of the University of Rome \La Sapienza". This conference was born in 1990 as a national meeting to be held every three years for Italian researchers in algorithms, data structures, complexity, and parallel and distributed computing. Due to a signi cant participation of foreign reaserchers, starting from the second conference, CIAC evolved into an international conference. In response to the call for papers for CIAC 2000, there were 41 subm- sions, from which the program committee selected 21 papers for presentation at the conference. Each paper was evaluated by at least three program committee members. In addition to the selected papers, the organizing committee invited Giorgio Ausiello, Narsingh Deo, Walter Ruzzo, and Shmuel Zaks to give plenary lectures at the conference. We wish to express our appreciation to all the authors of the submitted papers, to the program committee members and the referees, to the organizing committee, and to the plenary lecturers who accepted our invitation.