this book constitutes the refereed proceedings of the fourth international colloquium on grammatical inference, icgi-98, held in ames, iowa, in july 1998.the 23 revised full papers were carefully reviewed and selected for inclusion in the book from a total of 35 submissions. the book addresses a wide range of grammatical inference theory such as automata induction, grammar induction, automatic language acquisition, etc. as well as a variety of applications in areas like syntactic pattern recognition, adaptive intelligent agents, diagnosis, computational biology, data mining, and knowledge discovery.