Very recently, methods have been developed for studying the rates of c
hemical reactions between electrically neutral species in the gas phas
e at temperatures as low as 13 K. Here we review this exciting develop
ment in gas-phase chemical kinetics. Emphasis is placed on the importa
nce of the information which the experiments have provided, both from
the viewpoint of posing new questions about the factors which control
chemical reactivity and because of their relevance to the modelling of
molecular synthesis in interstellar clouds.