The 9th International Conference on Financial Cryptography and Data Security (FC 2005) was held in the Commonwealth of Dominica from February 28 to March 3, 2005. This conference, organized by the International Financial Cryptography Association (IFCA), continues to be the premier international forum for research, exploration, and debate regarding security in the context of finance and commerce. The conference title and scope was expanded this year to cover all aspects of securing transactions and systems. The goal is to build an interdisciplinary meeting, bringing together cryptographers, data-security specialists, business and economy researchers, as well as economists, IT professionals, implementers, and policy makers. We think that this goal was met this year. The conference received 90 submissions and 24 papers were accepted, 22 in the Research track and 2 in the Systems and Applications track. In addition, the conference featured two distinguished invited speakers, Bezalel Gavish and Lynne Coventry, and two interesting panel sessions, one on phishing and the other on economics and information security. Also, for the first time, some of the papers that were judged to be very strong but did not make the final program were selected for special invitation to our Works in Progress (Rump) Session that took place on Wednesday evening. Three papers were highlighted in this forum this year, and short versions of the papers are included here. As always, other conference attendees were also invited to make presentations during the rump session, and the evening lived up to its colorful reputation.