In the past decade, a number of orientational effects have been observed, produced by the passage of charged particles through crystals. These effects have a wide application in solid state physics, nuclear physics and the physics of hyperfine interactions. This book is not a survey but an introduction to this rapidly expanding branch of physics devoted to orientational effects and in particular to particle channelling in crystals. In it the authors discuss the interaction of charged particle beams with crystals and analyze the derivation of the fundamental equations describing this interaction. The channelling effect, the spatial redistribution of the particle flux and in the crystal lattice, and the problem of determining the position of an implanted atom in the lattice cell are also examined in detail. Student and postgraduate researchers as well as scientists and engineers working in experimental nuclear physics on the production of new materials and the physics of orientational effects, ion doping and solid state radiation physics may find this study useful.