Important Atomic and Molecular Processes in Galactic Chemistry

We discuss a variety of processes important in determining the chemical composition within interstellar and circumstellar clouds. Much of the gas-phase chemistry has been well-studied in the laboratory, although we point out several processes for which information is scarce. In recent years it has become apparent that grain surface chemistry plays a much bigger role in synthesising molecules than previously realized, and we discuss the chemistry of star-forming regions as a particular example of regions in which surface rather than gas chemistry may dominate.