This chapter deals with the concepts of orientation and alignment in atomic and molecular physics. The terms refer to parameters related to the shape and dynamics of an excited atomic or molecular level, as it is manifested in a nonstatistical population of the magnetic sublevels. To take full advantages of the possibilities of this approach, one utilizes third generation experiments, i.e., scattering experiments that exploit the planar scattering symmetry, contrary to an angular differential cross section determination (a second generation experiment) having cylindrical symmetry, or a total cross section measurement (a first generation experiment) integrating over all scattering angles. In this way, one is often able to probe atomic collision theories at a more fundamental level, and in favorable cases approach a perfect scattering experiment in which the complex quantal scattering amplitudes are completely determined. This term was coined by Bederson 1 and has since served as an ideal towards which scattering experiments attempt to strive.scattering theoryorientation and alignmentorientationalignmentcollisionorientation and alignment inpolarizationparticle scattering phenomenaperfect scattering experiment