Progress in the investigation of coordinatively unsaturated metal carbonyls by transient infrared spectroscopy is reviewed with an emphasis on gas phase studies. Typical current and possible future experimental methodologies are examined. The photophysics of production of coordinatively unsaturated metal carbonyls is discussed. Methods for the measurement of bond dissociation energies of transient species are reviewed, and the body of available data for coordinatively unsaturated metal carbonyls in the gas phase is presented. The current level of understanding of the factors that control the rate constants of ligand-metal carbonyl association reactions is discussed. Potential areas for future work are delineated.