This book constitutes the refereed proceedings of the 5th Internationa l Colloquium on Grammatical Inference, ICGI 2000, held in Lisbon, Port ugal in September 2000. The 24 revised full papers presented were care fully reviewed and selected from 35 submissions. The papers address to pics like machine learning, automata, theoretical computer science, co mputational linguistics, pattern recognition, artificial neural networ ks, natural language acquisition, computational biology, information r etrieval, text processing, and adaptive intelligent agents.