This chapter reviews some topics in classical electrodynamics that are fundamental for modern quantum optics and that appear throughout the remaining chapters, includingelectric dipole radiation, electromagnetic energy, Abraham and Minkowski momenta in dielectric media, photon momentum, and Rayleigh scattering. Other foundational topics treatedare Earnshaw’s theorem, gauges and Lorentz transformations of fields, radiation reaction, the Ewald-Oseen extinction theorem, different forms of stress tensors in dielectric media, and the optical theorem.