The course gives a very brief summary of longitudinal beam dynamics for both linear and circular accelerators. After discussing the synchronism conditions in linacs, it focuses on the particle motion in synchrotrons. It summarizes the equation of motions, discusses the phase space matching during a beam transfer, and introduces the Hamiltonian of the longitudinal motion.This paper gives a very brief summary of longitudinal beam dynamics for both linear and circular accelerators. After discussing synchronism conditions in linacs, it focuses on particle motion in synchrotrons. It summarizes the equations of motion, discusses phase-space matching during beam transfer, and introduces the Hamiltonian of longitudinal motion