In this chapter we will review the main methodological aspects providing the background for the computational study of thermochemical and spectroscopic properties of molecular systems. A variety of spectroscopies covering a large interval of the electromagnetic spectrum, from the radiofrequencies to the UV-Vis zones, have been applied to a selected set of molecular systems of interest in organometallic chemistry. Both isolated molecules in the gas and condensed phases and nanosystems have been studied, giving particular emphasis to the interplay between experiment and theory: stereoelectronic, vibrational, vibronic, and environmental effects are discussed for few illustrative examples. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.