In this chapter we revisit the interaction of matter and electromagnetic radiation with implications other than those connected to optical microscopy. Spectroscopy studies the interaction of matter with practically all forms of radiation. The main implication of such study is the chemical identification and/ or characterization of any kind of substance. The term spectroscopy is in fact quite generic, since it comprises different types of spectroscopies, each one linked to a specific type of radiation. Indeed, the interaction of matter with visible and ultraviolet light is the focus of study in electronic and Raman spectroscopy, whereas vibrational and rotational spectroscopy account for the interactions of matter with infrared (IR) and microwave radiation, respectively. Even radio waves are used to excite matter in nuclear magnetic resonance spectroscopy.