This work focuses on fundamental theoretical and experimental aspects of relativistic beam physics, recoil, and cooling phenomena in atomic and ion beams and traps, emphasizing coherence and collective effects. The physics of atomic laser and free electron laser, and the development of a bridge between them through the mechanism of the so-called recoil induced gain mechanism, is also examined, as are the links between relativistic beam physics and atomic laser physics. Topics include: laser cooling of trapped ions; optical lattices; spatio-temporal instabilities in optical systems; coherence in atom optics; coherent population trapping; two-level gain and collective recoil-induced effects; high-gain free electron laser - theory, experiments and projects; cooling of ion beams in a storage ring; and experiments on dense laser-cooled stored ion beams.