DLT 2005 was the 9th Conference on Developments in Language Theory. It was intended to cover all important areas of language theory, such us gr- mars, acceptors and transducers for strings, trees, graphs, and arrays; e?cient text algorithms; algebraic theories for automata and languages; combinatorial andalgebraicpropertiesofwordsand languages;variable-lengthcodes; symbolic dynamics; decision problems; relations to complexity theory and logic; picture descriptionandanalysis;polyominoesandbidimensionalpatterns;cryptography; concurrency; and DNA and quantum computing. DLT 2005 was held at Mondello (Palermo, Italy) during July 4-8, 2005 and was sponsored by the Department of "Matematica e Applicazioni," University of Palermo, the Department of "Informatica e Applicazioni - R.M. Capocelli," UniversityofSalerno, andtheMIURProject"Formal Languages and Automata: Methods, Models and Applications." The conference was also under the auspices of EATCS. We are grateful to these organizations. Previous DLTs were held in Turku (1993), Magdeburg (1995), Thessaloniki (1997), Aachen (1999), Vienna (2001), Kyoto (2002), Szeged (2003) and Auckland (2004). Since 2001, a DLT conference takes place in every odd year in Europe, and in every even year in another continent. The Program Committee selected 29 papers from 73 submitted papers. The papers came from the following countries: Austria, Belgium, Canada, Czech - public, Finland, France, Germany, India, Italy, Portugal, Moldova, Russia, Spain, and the UK. Each submitted paper was evaluated by at least three members of theProgramCommittee, whowereoftenassistedbytheirreferees.All29selected papers are contained in this volume together with 6 invited presentations.