The book is devoted to processes at the interaction of high energy charged particles and photons with crystals. Among them are the creation of electron-positron pair by photon in crystalline field, the radiation of particles in this field and, connected with these effects, the new type of electromagnetic showers in crystals, the channeling of fast particles in crystal and channeling radiation. At high energies, the processes of quantum electrodynamics (QED) in intense external fields play an important role in crystals. The first third of the book contains a new formulation of QED in external fields which is valid for any external field, including an essentially nonuniform one and has vast applications.