The Fifth International Colloquium on Grammatical Inference (ICGI-2000) was heldinLisbononSeptember11-13th,2000.ICGI-2000wasthe?fthinaseriesof successfulbiennialinternationalconferencesintheareaofgrammaticalinference. Previous conferences were held in Essex, U.K.; Alicante, Spain; Montpellier, France; and Ames, Iowa, USA. This series of meetings seeks to provide a forum for the presentation and discussion of original research on all aspects of grammatical inference. Gram- tical inference, the process of inferring grammar from given data, is a ?eld that is not only challenging from a purely scienti?c standpoint but also ?nds many applications in real world problems. Despitethefactthatgrammaticalinferenceaddressesproblemsinarelatively narrow area, it uses techniques from many domains, and intersects a number of di?erent disciplines. Researchers in grammatical inference come from ?elds as diverse as machine learning, theoretical computer science, computational ling- stics, pattern recognition and arti?cial neural networks. From a practical standpoint, applications in areas such as natural language acquisition, computational biology, structural pattern recognition, information retrieval, text processing and adaptive intelligent agents have either been - monstrated or proposed in the literature. ICGI-2000 was held jointly with CoNLL-2000, the Computational Natural Language Learning Workshop and LLL-2000, the Second Learning Language in LogicWorkshop.Thetechnicalprogramincludedthepresentationof24accepted papers (out of 35 submitted) as well as joint sessions with CoNLL and LLL. A tutorial program organized by Gabriel Pereira Lopes took place after the meetings and included tutorials by Raymond Mooney, Gregory Grefenstette, Walter Daelemans, Ant' onio Ribeiro, Joaquim Ferreira da Silva, Gael Dias, Nuno Marques,VitorRossio,Jo" aoBalsaandAlexandreAgostini.Thejointrealization of these events represents a unique opportunity for researchers in these related ?elds to interact and exchange ideas.