This volume contains the papers presented at ESA 2009: The 17th Annual - ropean Symposium on Algorithms, September 7-9, 2009. ESA has been held annually since 1993, and seeks to cover both theoretical and engineering aspects of algorithms. The authors were asked to classify their paper under one or more categories as described in Fig. 1. Since 2001, ESA has been the core of the larger ALGO conference, which typically includes several satellite conferences. ALGO 2009 was held at the IT University of Copenhagen, Denmark. The ?ve members of the ALGO 2009 - ganizing Committee were chaired by Thore Husfeldt. The ESA submission deadline was April 12, Easter Sunday. This was clearly an error and we o?er profuse apologies for this mistake. Albeit no excuse, the hard constraints we faced were (a) ICALP noti?cation, April 6, and (b) ESA in Copenhagen, September 7. Between these two endpoints we needed to design a schedule that allowed modifying ICALP rejections for resubmission (1 week), Program Committee deliberations (7 weeks), preparing ?nal versions (4 weeks), and, to prepare, publish, and transport the proceedings (9 weeks). ESA 2009had 272submissions ofwhich 14 werewithdrawn overtime. Of the remaining 222 submissions to Track A (Design and Analysis), 56 were accepted. Of the remaining 36 submissions to Track B (Engineering and Applications), 10 were accepted. This gives an acceptance rate of slightly under 25%.

This coherent anthology presents the state of the art in the booming area of online algorithms and competitive analysis of such algorithms. The 17 papers are carefully revised and thoroughly improved versions of presentations given first during a Dagstuhl seminar in 1996.
An overview by the volume editors introduces the area to the reader. The technical chapters are devoted to foundational and methodological issues for the design and analysis of various classes of online algorithms as well as to the detailed evaluation of algorithms for various activities in online processing, ranging from load balancing and scheduling to networking and financial problems. An outlook by the volume editors and a bibliography listing more than 750 references complete the work.
The book is ideally suited for advanced courses and self-study in online algorithms. It is indispensable reading for researchers and professionals active in the area.