Publisher Summary This chapter discusses collision experiments using laser excited atoms in crossed beams. With the advent of tunable narrow-band lasers, especially cw dye lasers, the situation has changed and it has become clear that it should be possible to excite atoms optically within the scattering region of an otherwise conventional crossed-beam experiment. In this way a steady-state upper-state population could be reached that may be comparable to the ground-state population. When an atomic beam is excited, it is free of internal collisions and, for right angle intersection with the laser, free of Doppler broadening. Then the laser properties allow selecting the state into which the atom is excited. Specific fine- and hyperfine-structure states may be chosen as well as a particular combination of sub-states. The novel techniques allow preparing states with an angular momentum different from zero and to vary systematically the alignment and orientation of the resulting non-spherical interaction potentials. Frequency doubling of dye lasers can also widen the scale of possible applications. Very high powers are needed and one probably would have to use a pulsed laser. An alternative to frequency doubling is the direct two-photon excitation of atoms.