The Ninth International Conference on Reliable Software Technologies, Ada- Europe 2004, took place in Palma, Spain, June 14-18, 2004. It was sponsored by Ada-Europe, the European federation of national Ada societies, and Ada- Spain, in cooperation with ACM SIGAda. It was organized by members of the University of the Balearic Islands (UIB). As in past years, the conference comprised a three-day technical program, during which the papers contained in these proceedings were presented, along with vendor presentations. The technical program was bracketed by two tutorial days, when the attendees had the opportunity to catch up on a variety of topics related to the ?eld, at both introductory and advanced levels. Furthermore, the conference was accompanied by an exhibition where vendors presented their products for supporting reliable-software development. Invited Speakers Theconferencepresentedfourdistinguishedspeakers,whodeliveredstate-of-t- art information on topics of great importance, both for now and for the future of software engineering: - S. Tucker Taft, SoftCheck Inc., USA Fixing software before it breaks: using static analysis to help solve the so- ware quality quagmire - Martin Gogolla, University of Bremen, Germany Bene?ts and problems of formal methods - Antoni Oliv´ e, Polytechnical University of Catalonia, Spain On the role of conceptual schemas in information systems' development - Stephen Vinoski, IONA Technologies in Waltham, USA Can middleware be reliable? Wewouldliketoexpressoursinceregratitudetothesedistinguishedspeakers, well known to the community, for sharing their insights with the conference participants. Submitted Papers Alargenumberofpapersweresubmitted,fromasmanyas15di?erentcountries.