This talk reviews some of the basic concepts in cold collisions, and gives examples of calculations directed towards understanding the following areas: (1) collisions of Na atoms trapped in Zeeman components of theF=1hyperfine sublevel, and their control by magnetically-induced Feshbach resonances; (2) elastic and inelastic collisions of Cs atoms in the double spin-polarizedF=4,M=4level; and (3) stimulated Raman photoassociation of two colliding atoms in a Bose-Einstein condensate (BEC) to make translationally cold molecules in a selected target level. ©1999 American Institute of Physics.