Understanding ceramic processes requires simultaneous consideration of the thermodynamics of chemical equilibrium and the kinetic limitations on the attainment of equilibrium imposed through finite atomic mobilities and the probabilistic nature of complex phase formation. The equilibrium phase diagram, its thermodynamic basis and interpretation are considered here as effecting processing decisions in raw materials selection and processes before firing, as well as in optimization of process tempertaures for reaction and sintering for the development of unique microstructures. Consideration of long-term environmental and thermal equilibration are also discussed, particularly in electronic materials for sensor devices as well as conventional refractory applications.