This book presents a systematic and coherent approach to phase transitions and critical phenomena, namely the coherent-anomaly method (CAM theory) based on cluster mean-field approximations. The first part gives a brief review of the CAM theory and the second part a collection of reprints covering the CAM basic calculations, the Blume-Emery-Griffiths model, the extended Baxter model, the quantum Heisenberg model, zero-temperature phase transitions, the KT-transition, spin glasses, the self-avoiding walk, contact processes, branching processes, the gas-liquid transition and even non-equilibrium phase transitions.