The number of organometallic compounds containing heteronuclear metal–metal bonds has grown tremendously in the last ten years. Also known as cluster compounds, these compounds have been found to exhibit a rich diversity of molecular structures and reactivities. Descriptions of the structures and transformations of the complexes are central features. Separate chapters have been prepared for compounds containing bonds between transition metals and the metals of the copper and zinc subgroups. Unlike COMC, this volume contains an entire chapter devoted to studies of heteronuclear metal compounds in catalysis.