Almost the whole of astrophysics is based on the interpretation of electromagnetic radiation reaching us from space. This interpretation rests on our fundamental knowledge of how em radiation interacts with electrons, atoms and molecules. Atomic and molecular physics, important in many astrophysical processes, is therefore extensively covered in this course. Contents: type of spectra, blackbody radiation, Thomson, Compton and inverse Compton scattering, Rayleigh scattering, fluorescence, detailed balance, Einstein-Milne relations, time-dependent perturbation theory, transition probabilities, selection rules, forbidden transitions, population inversion, astrophysical masers.