This book constitutes the refereed proceedings of the 21st AnnualSymposium on Combinatorial Pattern Matching, CPM 2010, held in New York, USA, in June 2010.The 28 revised full papers presented together with 3 invited talks werecarefully reviewed and selected from 53 submissions. The papers addressall areas related to combinatorial pattern matching and itsapplications, such as searching and matching strings and morecomplicated patterns such as trees, regular expressions, graphs, pointsets, and arrays with special focus on coding and data compression, computational biology, data mining, information retrieval, naturallanguage processing, pattern recognition, string algorithms, stringprocessing in databases, symbolic computing and text searching.