Book excerpt: Nonadiabatic transition is a highly multidisciplinary concept and phenomenon, constituting a fundamental mechanism of state and phase changes in various dynamical processes of physics, chemistry and biology, such as molecular dynamics, energy relaxation, chemical reaction, and electron and proton transfer. Control of molecular processes by laser fields is also an example of time-dependent nonadiabatic transition. In this new edition, the original chapters are updated to facilitate enhanced understanding of the concept and applications. Three new chapters OCo comprehension of nonadiabatic chemical dynamics, control of chemical dynamics, and manifestation of molecular functions OCo are also added.