Mononuclear. binuclear, and trinuclear transition-metal allenyl and/or propargyl complexes are reviewed with respect to methods of synthesis, structure, and reaction chemistry. Structural relationships among the various types of complexes are presented and, to the extent possible, used to rationalize some patterns of reactivity. Recent developments in the field are accorded special emphasis. (C) 2002 Elsevier Science B.V. All rights reserved.