This book constitutes the refereed proceedings of the Third Latin American Symposium on Theoretical Informatics, LATIN'98, held in Campinas, Brazil, in April 1998. The 28 revised full papers presented together with five invited surveys were carefully selected from a total of 53 submissions based on 160 referees' reports. The papers are organized in sections on algorithms and complexity; automata, transition systems and combinatorics on words; computational geometry and graph drawing; cryptography; graph theory and algorithms on graphs; packet routing; parallel algorithms; and pattern matching and browsing.