The papers in this volume were presented at the Third Workshop on Algorithmsand Data Structures (WADS '93), held in Montreal, Canada, August 1993. The volume opens with five invited presentations: "Computing the all-pairs longest chains in the plane" by M.J. Atallah and D.Z. Chen, "Towards a better understanding of pure packet routing" by A. Borodin, "Tolerating faults in meshes and other networks" (abstract) by R. Cole, "A generalization of binary search" by R.M. Karp, and "Groups and algebraic complexity" (abstract) by A.C. Yao. The volume continues with 52 regular presentations selected from 165 submissions, each of which was evaluated by at least three program committee members, many of whom called upon additional reviewers.

Symposium on Algorithms (ESA '93), held in Bad Honnef, near Boon, in Germany, September 30 - October 2, 1993. The symposium is intended to launchan annual series of international conferences, held in early fall, covering the field of algorithms. Within the scope of the symposium lies all research on algorithms, theoretical as well as applied, that is carried out in the fields of computer science and discrete applied mathematics. The symposium aims to cater to both of these research communities and to intensify the exchange between them. The volume contains 35 contributed papers selected from 101 proposals submitted in response to the call for papers, as well as three invited lectures: "Evolution of an algorithm" by Michael Paterson, "Complexity of disjoint paths problems in planar graphs" by Alexander Schrijver, and "Sequence comparison and statistical significance in molecular biology" by Michael S. Waterman.

The papers in this volume were presented at SWAT 92, the Third Scandinavian Workshop on Algorithm Theory. The workshop, which continues the tradition ofSWAT 88, SWAT 90, and the Workshop on Algorithms and Data Structures (WADS 89, WADS 91), is intended as an international forum for researchers in the area of design and analysis of algorithms. The volume contains invited papers by L.G. Valiant (Direct bulk-synchronous parallel algorithms), A.A. Razborov (On small depth threshold circuits), G. Gonnet (Efficient two-dimensional searching), and E. Welzl (New results on linear programming and related problems), together with 34 selected contributed papers. Contributions cover algorithms and data structures in all areas, including combinatorics, computational geometry, data bases, parallel and distributed computing, and graphics.

The Workshop on Approximation and Online Algorithms (WAOA 2003) focused on the design and analysis of algorithms for online and computationally hard problems. Both kinds of problems have a large number of applications ar- ing from a variety of ?elds. The workshop also covered experimental research on approximation and online algorithms. WAOA 2003 took place in Budapest, Hungary, from September 16 to September 18. The workshop was part of the ALGO 2003 event, which also hosted ESA 2003, WABI 2003, and ATMOS 2003. TopicsofinterestforWAOA2003were:competitiveanalysis,inapproximab- ityresults,randomizationtechniques,approximationclasses,scheduling,coloring and partitioning, cuts and connectivity, packing and covering, geometric pr- lems, network design, and applications to game theory and ?nancial problems. In response to our call for papers we received 41 submissions. Each submission was reviewed by at least 3 referees, who judged the papers on originality, quality, and consistency with the topics of the conference. Based on these reviews the program committee selected 19 papers for presentation at the workshop and for publication in this proceedings. This volume contains the 19 selected papers and 5 invited abstracts from an ARACNE minisymposium which took place as part of WAOA.

This symposium is jointly sponsored by the ACM Special Interest Group on Algorithms and Computation Theory and the SIAM Activity Group on Discrete Mathematics.