This course is an introduction to atomic physics. It concerns to apply approximation methods (such as time dependent, time-independent perturbation theory) to many perturbed problems in quantum mechanics as well as in atomic physics. Examples of these problems: interaction of one-electron atoms in electric and magnetic fields, interaction of one-electron atoms with electromagnetic radiation. Studying the transition rate and the selection rules as well as the spectrum for one-electron atoms. Finally, studying two and many-electron atoms.