This book constitutes the refereed proceedings of the 15th European Conference on Object-Oriented Programming, ECOOP 2001, held in Budapest, Hungary, in June 2001. The 18 revised full papers presented together with one invited paper were carefully reviewed and selected from 108 submissions. The book is organized in topical sections on sharing and encapsulation, type inference and static analysis, language design, implementation techniques, reflection and concurrency, and testing and design.