This textbook explains the basic principles of high-energy crystal channeling physics and introduces a non-specialist into the bent-crystal applications at accelerators. It covers topics such as charged particle channeling in straight and bent crystals, different mechanisms of particle trap into channeling mode, theory of dechanneling, computer simulations, and effects of crystal lattice distortions. It deals with crystal bending methods, and experimental schemes are discussed in detail and compared to the theory. The second half of the text considers the crystal applications: beam extraction, splitting, focusing, diagnostics etc.