In retrospect, it was obvious that we were both, quite inde pendently, contemplating a conference on the role of molybdenum in biology and related chemistry. At the time though, the meeting of minds on this matter was quite surprising. Although this subject has been treated in previous meetings within the overall context of, say, magnetic resonance or nitrogen fixation, it was apparent to us both that research in molybdenum-containing enzymes and molyb denum chemistry had progressed rapidly in the last several years. Jointly, we decided to organize the first meeting on Molybdenum Chemistry of Biological Significance which was held at the Hotel Lake Biwa, Shiga, Japan, on April 10-13, 1979. This volume con stitutes the Proceedings of that international conference and covers the broad spectrum of interests from enzymes to coordination chemistry. It should serve not only as a source of new information on the latest research results in this area and as a useful ref erence tool, but should also allow a newcomer or other peripherally interested researcher to become conversant very rapidly with the "state-of-the-art" in this specialized and important area of research. The conference was sponsored by the Japan Society for the Promotion of Science, the Japan World Exposition Commemerative Fund the Yamada Science Foundation, the Nissan Science Foundation, the Chemical Society of Japan (Kinki Regional Office) and the Agri cultural Chemical Society of Japan (Kansai Branch). We thank these organizations sincerely for their interest and generosity.