For the ?fth time in its history, in cooperation with Springer-Verlag, the European C- ference on Object-Oriented Programming (ECOOP) conference series is glad to offer the object-oriented research community the ECOOP 2001 Workshop Reader, a c- pendium of workshop reports, panel transcripts, and poster abstracts pertaining to the ECOOP 2001 conference, held in Budapest from 18 to 22 June, 2001. ECOOP 2001 hosted 19 high-quality workshops covering a large spectrum of - search topics. The workshops attracted 460 participants on the ?rst two days of the conference. Originally 22 workshops were chosen from 26 proposals by a workshop selection committee, following a peer review process. Due to the overlaps in the areas of interest and the suggestions made by the committee six of the groups decided to merge their topicsintothreeworkshops.Thisbookcontainsinformationonthepanel,postersession, and 17 workshop reports, for which we have to thank our workshop organizers, who did a great job in preparing and formatting them. The reports are organized around the main line of discussion, comparing the - rious approaches and giving a summary on the debates. They also include the list of participants, af?liations, contact information, and the list of contributed position papers. Although they usually do not include abstracts or excerpts of the position papers, they do give useful references to other publications and websites, where more information may be found.