Brian Johnson has made important contributions to transition metal chemistry. His early work was concerned with the chemistry of nitrosyl complexes and the reactivity of the coordinated nitric oxide group. Subsequent work was concerned with the structure and reactivity of simple organic molecules coordinated to a metal centre, particularly those containing unsaturated carbon centres. The emphasis of his more recent work has been in the field of polynuclear carbonyl complexes, particularly in ruthenium and osmium. A wide range of new bonding modes for both metal and ligand groups have been identified and the general stereochemical properties of the metal polyhedron have been rationalised in terms of a model depending upon the packing of the coordinated carbonyl groups. This model has been extended to account for the fluxionality observed in these complexes. Brian has been responsible, in part, for the rapid development of cluster chemistry and the recognition of the difference in the properties of these complexes from mononuclear species.