This document contains the proceedings of a joint meeting of the International Federation for Medical and Biological Engineering and the International Organization for Medical Physics. Participants from over 50 countries were in attendance. The theme of the program, "Challenges for the Year 2000," was a reminder of the challenges which confront the world community; specifically, better, more widely distributed, and less expensive health care, and a continuing concern for the well being of humanity and of the earth. The proceedings contain abstracts from over 200 papers, speeches, and sessions, and is organized into medical physics and biomedical engineering sections. (CW)