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%.