The section devoted to iron in this volume reflects the tremendous progress in the area. Specifically cluster chemistry, ligand transformations and detailed structural results are more prominent in COMC II . The organic chemistry of ruthenium and osmium is an area which has burgeoned during the period since the publication of COMC . This is especially true for the cluster chemistry of these elements, which have provided most of the advances in this important field. Consequently, this volume will include an update (1981-1993) of the chemistry of mono- and bi-nuclear complexes of ruthenium and osmium, with a rather more extensive treatment of tri- and tetra-nuclear complexes. This is because many of the early results in ruthenium and osmium cluster chemistry described in COMC are now much better understood and can thus be placed in a more general context. In the case of complexes containing clusters with five or more metal atoms, the coverage is essentially complete, again because this chemistry has developed during the 1980s.