Crossed beam experiments

Many natural phenomena can only be properly understood if we have a detailed knowledge of interactions involving atoms, molecules, ions, electrons or photons. In the laboratory these processes are often studied by preparing beams of two types of particle and observing the reactions which occur when the beams intersect. Some of the more interesting of these crossed beam experiments and their results will be discussed. Propods to extend colliding beam techniques to high energy particle physics will also be outlined.