This volume contains papers presented at the firstinternational workshop onword equations and related topicsheld at the University of T}bingen in October 1990. Wordequations, the central topic of this annual workshop, lieatthe intersection of several important areas of computerscience, suchas unification theory, combinatorics on words,list processing, and constraint logic programming. Theworkshop is a forum where researchers fromthese differentdomains may present and discuss results and ideas, therebysupporting interaction and cross-fertilization betweentheoretical questions and practical applications. The volumecollects papers which:- contain new and relevant results,- describe a new approach to a subject, or- give a survey of main developments in an area.Papers cover investigations on free groups, associativeunification and Makanin's algorithm to decide thesolvability of equations in free semigroups, generalunification theory and its relationship to algebra and modeltheory, Thue systems, and finitely presented groups.