The papers contained in this volume were presented at the 21st Annual S- posium on Combinatorial Pattern Matching (CPM 2010) held at NYU-Poly, Brooklyn, New York during June 21-23, 2010. Allthe paperspresentedatthe conferenceareoriginalresearchcontributions. We received 53 submissions from 21 countries. Each paper was reviewed by at least three reviewers. The committee decided to accept 28 papers. The program also includes three invited talks by Zvi Galil from Tel Aviv University, Israel, Richard M. Karp from University of California at Berkeley, USA, and Je?rey S. Vitter from Texas A&M University, USA. The objective of the annual CPM meetings is to provide an international forum for research in combinatorial pattern matching and related applications. It addresses issues of searching and matching strings and more complicated p- terns such as trees, regular expressions, graphs, point sets, and arrays. The goal is to derive non-trivialcombinatorialproperties of suchstructures and to exploit these properties in order to either achieve superior performance for the cor- sponding computational problems or pinpoint conditions under which searches cannot be performed e?ciently. The meeting also deals with problems in c- putational biology, data compression and data mining, coding, information - trieval, natural language processing and pattern recognition. TheAnnual SymposiumonCombinatorialPatternMatchingstartedin 1990, andhassincetakenplaceeveryyear.PreviousCPM meetingswereheld inParis, London, Tucson, Padova, Asilomar, Helsinki, Laguna Beach, Aarhus, Pisc- away, Warwick, Montreal, Jerusalem, Fukuoka, Morelia, Istanbul, Jeju Island, Barcelona, London, Ontario, Pisa, and Lille.