A concise introduction to the spectroscopy of atoms and molecules. Treatment emphasizes an intuitive understanding of topics and the development of problem-solving techniques. Provides background material on time-dependent perturbation theory and second quantization, and incorporates many illustrative spectra from the literature. Examines electronic band spectra and polyatomic rotations, which makes accessible the energy levels and selection rules that govern microwave spectroscopy without recourse to detailed rotational eigenstates. Also covers triatomic molecules, aromatic hydrocarbons, lasers, multiphoton spectroscopies, and diagrammatic perturbation techniques.