Dlt 2001 Was The ?fth Conference On Developments In Language Theory. It Was A Broadly Based Conference Covering All Aspects Of Language Theory: Grammars And - Ceptorsforstrings,graphs,arrays,etc. ;ef?cientalgorithmsforlanguages;combinatorial Andalgebraicpropertiesoflanguages;decisionproblems;relationstocomplexitytheory; Logic; Picture Description And Analysis; Dna Computing; Cryptography; Concurrency. Dlt 2001 Was Held At Technische Universitat ยจ Wien From July 16 To July 21, 2001. The Organizingcommitteeconsistedofrudolffreund,wernerkuich(chairman),christiane Nikoll, Margarethe Soukup, Friedrich Urbanek. Previous Dlts Were Held In Turku (1993), Magdeburg (1995), Thessalonike (1997), Aachen (1999). The Program Committee Of Dlt 2001 Consisted Of Christian Choffrut (paris), Jยจ Urgen Dassow (magdeburg), Masami Ito (kyoto), Werner Kuich (wien, Chairman),giancarlomauri(milano),gheorghepaun ? (bucuresti), ยธ Grzegorzrozenberg (leiden), Arto Salomaa (turku), Wolfgang Thomas (aachen). It Selected 24 Papers From 64 Papers Submitted In Response To The Call For Papers. These Papers Came From The Following Countries: Australia, Austria, Belgium, Brazil, Bulgaria, Canada, Czech Republic, Estonia, Finland, France, Germany, Hungary, India, Italy, Japan, Moldova, The Netherlands, Phillipines, Poland, Romania, Russia, Slovakia, Spain, United Kingdom, Usa. Each Submitted Paper Was Evaluated By At Least Four Members Of The Program Committee. Together With 10 Invited Presentations All 24 Selected Papers Are Contained In This Volume. The Papers In This Volume Are Printed According To The Order Of Presentation At Dlt 2001 And Thus Grouped Into Sessions, Most Of Which Are Thematic. It Is A Pleasure For The Editors To Thank The Members Of The Program Committee For The Evaluation Of The Papers, And The Many Referees Who Assisted In This Process. Automata: From Uncertainty To Quantum / C.s. Calude And E. Calude -- Elementary Theory Of Ordinals With Addition And Left Translation By [omega] / C. Choffrut -- The Equational Theory Of Fixed Points With Applications To Generalized Language Theory / Z. Esik -- Second-order Logic Over Strings: Regular And Non-regular Fragments / T. Eiter, G. Gottlob And T. Schwentick -- Decision Questions On Integer Matrices / T. Harju -- Some Petri Net Languages And Codes / M. Ito And Y. Kunimoch -- Words, Permutations, And Representations Of Numbers / H. Prodinger -- Proof Complexity Of Pigeonhole Principles / A.a. Razborov -- Words And Patterns / A. Restivo And S. Salemi -- A Short Introduction To Infinite Automata / W. Thomas. Werner Kuich, Grzegorz Rozenberg, Arto Salomaa (eds.). Includes Biographical References And Index.