  This paper reviews the chemistry of star-forming regions, with an emphasis on
the formation of high-mass stars. We first outline the basic molecular
processes in dense clouds, their implementation in chemical models, and
techniques to measure molecular abundances. Then, recent observational,
theoretical and laboratory developments are reviewed on the subjects of hot
molecular cores, cosmic-ray ionization, depletion and deuteration, and oxygen
chemistry. The paper concludes with a summary of outstanding problems and
future opportunities.
