A composition suitable for use as a catalyst for the reaction of an isocyanate compound or prepolymer thereof with an alcohol to form a polyurethane comprises a mixture of (a)an organometallic compound selected from: (i) a compound of formula M(RO).sub.4, where M is titanium, zirconium, hafnium, aluminium, cobalt or iron or a mixture of these metals and OR is the residue of an alcohol ROH in which R comprises an (optionally substituted) C.sub.1-30 cyclic, branched or linear, alkyl, alkenyl, aryl or alkyl-aryl group or a mixture thereof, or; (ii) a complex of titanium, zirconium and/or hafnium and an acetoacetate ester and (b) a coordinating compound selected from a ketone, aldhehyde, carboxylic acid, sulphonic acid, nitride or an imine. An isocyanate composition containing a catalyst of the claimed composition is also described.