The refereed proceedings of the 7th International Conference on Developments in Language Theory, DLT 2003, held in Szeged, Hungary, in July 2003. The 27 revised full papers presented together with 7 invited papers were carefully reviewed and selected from 57 submissions. All current aspects in language theory are addressed, in particular grammars, acceptors, and transducers for strings, trees, graphs, arrays, etc; algebraic theories for automata and languages; combinatorial properties of words and languages; formal power series; decision problems; efficient algorithms for automata and languages; and relations to complexity theory and logic, picture description and analysis, DNA computing, quantum computing, cryptography, and concurrency.