Chemistry in quiescent and star-forming molecular clouds

Recent advances in astrochemistry are discussed and illustrated with examples obtained with new submillimeter and infrared facilities. Simple molecules such as H-3(+), H2D+, CH+, CH3, H2O and O-2 provide tests of the basic hydrogen-,, carbon- and oxygen chemical networks, as well as clues to the physical structure of molecular clouds. Systematic observations of high-mass star-forming regions allow the chemical evolution from collapsing clouds to hot cores and ultracompact H II regions to be traced. Chemical diagnostics at different wavelengths are identified and the prospects for future observations are discussed.