This book constitutes the thoroughly refereed post-proceedings of the 5th International Conference on Developments in Language Theory, DLT 2001, held in Vienna, Austria, in July 2001. The 24 revised full papers presented together with 10 revised invited papers were carefully selected during two rounds of reviewing and revision from a total of 64 papers submitted. Among the topics covered are grammars and acceptors, efficient algorithms for languages, combinatorial and algebraic properties, decision problems, relations to complexity theory, logic, picture description and analysis, DNA computing, cryptography, and concurrency.