Practical applications of the cuprates depend heavily on the coherence of their superconducting state. Introductory chapters of this book present the special problems posed by the strong anisotropy of the cuprates. They are followed by pedagogical reviews on fluctuation effects, the properties of the vortex state, physics of tunneling (s and d-wave superconductors), and properties of related junction devices. Preparation methods and advanced experiments on state of the art single crystals and thin films are emphasized.