The 7th Workshop on Approximation and Online Algorithms (WAOA 2009) focused on the design and analysis of algorithms for online and computati- ally hard problems. Both kinds of problems have a large number of applications from a variety of ?elds. WAOA 2009 took place in Copenhagen, Denmark, d- ing September 10-11, 2009. The workshop was part of the ALGO 2009 event that also hosted ESA 2009, IWPEC 2009, and ATMOS 2009. The previous WAOA workshops were held in Budapest (2003), Rome (2004), Palma de M- lorca(2005),Zurich(2006),Eilat(2007),andKarlsruhe(2008).The proceedings ofthesepreviousWAOAworkshopshaveappearedasLNCSvolumes2909,3351, 3879, 4368, 4927, and 5426, respectively. Topics of interest for WAOA 2009 were: algorithmic game theory, appr- imation classes, coloring and partitioning, competitive analysis, computational ?nance, cuts and connectivity, geometric problems, inapproximability results, mechanism design, network design, packing and covering, paradigms for design and analysis of approximationand online algorithms,parameterizedcomplexity, randomization techniques, real-world applications, and scheduling problems.
In response to the call for papers, we received 62 submissions. Each subm- sionwasreviewedbyatleastthreereferees,andthevastmajoritybyatleastfour referees. The submissions were mainly judged on originality, technical quality, andrelevanceto the topics of the conference.Basedon the reviews,the Program Committee selected 22 papers. We are grateful to Andrei Voronkov for providing the EasyChair conference system,whichwasusedtomanagetheelectronicsubmissions,thereviewprocess, and the electronic PC meeting. It made our task much easier. We would also like to thank all the authors who submitted papers to WAOA 2009 as well as the local organizers of ALGO 2009.