Field ion mass spectrometry is capable of analyzing individual particles from a solid surface with a geometrical resolution of several Å 2 within the area of a single crystal plane. The application of field pulses allows kinetic measurements of surface reactions to be made in the μsec time scale. The chemisorption, adsorption and reaction of S 2 molecules (S 2 ⇌ S χ→ S 8) on different metal surfaces represent a field-independent reaction type. The behavior of sulphur on Ag, Pt, and W surfaces will be described in detail. Remarkable field effects on chemical surface reactions are observed during the interaction of different gases (such as H 2O, NH 3, C 2 H 4, CO, O 2, etc.) with silver surfaces. The formation of metal complex ions resembles processes that are well known in electrochemical electrode reactions. Another mechanism of ion formation is closely linked to the stability of carbonium ions, which are either formed by heterolytic bond cleavage or byprotonattachment processes. Exampleswill be given for different hydrocarbons. Additional information on the energetics of surface reactions forming field ions is obtained by the energy analysis of charged particles. The measurement of appearance potentials allows discrimination between different possible reaction pathways. The advantages and difficulties for analyzing surface composition and surface reactions by field ion mass spectrometry are discussed.