Chapter 5 uses concepts of diffusion and nucleation to understand phase transformations in ways beyond a simple usage of equilibrium phase diagrams. A number of nonequilibrium phenomena are described, which show how to understand some phase transformations that have impediments from nucleation and diffusion. In general, the slowest processes are first to cause deviations from states of equilibrium. For faster heating or cooling, however, sometimes the slowest processes are fully suppressed, and the next-slowest processes become important. Nonequilibrium processes in alloy freezing are explained, as is the glass transition. Approximately, Chapter 5 progresses from slower to faster kinetic processes. However, the last section discusses why kinetic processes based on activated state rate theory should bring materials to thermodynamic equilibrium.