The papers in this volume were selected for presentation at the 15th Annual InternationalComputing and CombinatoricsConference (COCOON 2009), held during July 13-15, 2009 in Niagara Falls, New York, USA. Previous meetings of this conference were held in Xian (1995), Hong Kong (1996), Shanghai (1997), Taipei(1998), Tokyo(1999), Sydney(2000), Guilin(2001), Singapore(2002), Big Sky (2003), Jeju Island (2004), Kunming (2005), Taipei (2006), Alberta (2007), and Dalian (2008). In response to the Call for Papers, 125 extended abstracts (not counting withdrawn papers) were submitted from 28 countries and regions, of which 51 were accepted. Authors of the submitted papers were from Cyprus (1), The Netherlands (1), Bulgaria (1), Israel (1), Vietnam (2), Finland (1), Puerto Rico (2), Australia (4), Norway (4), Portugal (1) Spain (2), France (16), Republic of Korea(3), Singapore(2), Italy(6), Iran, (4), Greece(7), Poland(4), Switzerland (8), Hong Kong (10), UK (12), India (7), Taiwan (18), Canada (23), China (19), Japan (39), Germany (44), and the USA (77). The submitted papers were evaluated by an international Technical P- gram Committee (TPC) consisting of Srinivas Aluru (Iowa State University, USA), Lars Arge (University of Aarhus, Denmark), Vikraman Arvind (Ins- tute of Mathematical Sciences, India), James Aspnes (Yale University, USA), Mikhail Atallah (Purdue University, USA), Gill Barequet (Technion - Israel - stitute of Technology, Israel), Michael Brudno (University of Toronto, Canada), Jianer Chen (Texas A&M, USA), Bhaskar DasGupta (University of Illinois at Chicago, USA), Anupam Gupta (Carnegie Mellon University, USA), Lane A.