Controlling chemical reactions with light rests on the idea of exciting a vibration that becomes the reaction coordinate in subsequent chemistry. Vibrational excitation techniques such as infrared or stimulated Raman excitation of fundamental vibrations or vibrational overtone excitation of higher levels permit the preferential cleavage of a bond in a photodissociation or bimolecular reaction. The key to bond-selected chemistry is the initial preparation of a suitable vibrational state followed, in the case of bond-selected photodissociation, by electronic excitation or, in the case of bond-selected bimolecular reaction, by collision with a reactive atom. Such experiments demonstrate bond-selected chemistry, permit detailed comparison to theory, and reveal general principles of vibrational state control of chemical reactions.