This book constitutes the proceedings of the 14th International Conference on Developments in Language Theory, DLT 2010, held in London, Ontario, Canada, in August 2010. The 32 regular papers presented were carefully reviewed and selected from numerous submissions. The volume also contains the papers or abstracts of 6 invited speakers, as well as a 2-page abstract for each of the 6 poster papers. The topics addressed are formal languages, automata theory, computability, complexity, logic, petri nets and related areas.