This book discusses the effect of the excitation of rotational, vibrational, and electronic degrees of freedom on the basic electrical properties of molecules and, as a consequence, on molecular optical and transport properties together with reactivity. It additionally summarizes the theory and practice of calculating state-specific electric and optical properties based on ab initio quantum chemical calculations. The book offers a clear, up-to-date review and is primarily intended for actively working researchers, graduate students, and advanced undergraduates who are interested in the electric and related properties of the electronically, rotationally, and vibrationally excited molecules.