Publisher Summary This chapter focuses on spectroscopy (especially, infrared spectroscopy) that has been a widely used technique in the industry for the structural and compositional analysis of organic, organometallic, metalorganic, inorganic, and polymeric materials, in addition to quality control of raw materials and commercial products. Spectroscopic techniques are concerned with the interaction between radiation of some sort and matter, using radiation with an energy or wavelength appropriate to the distance and time scales relevant to the microscopic study of atoms, molecules, and solids. A large number of radiation types can be used: electromagnetic radiation, elementary particles, nuclei, ions, and ultrasonic waves. The chapter discusses infrared and Raman spectroscopy, which are vibrational spectroscopic techniques and describes spectroscopy based on interactions between X-rays and electrons and a sample. In-situ spectroscopic methods, such as heating stage Raman spectroscopy and infrared emission spectroscopy, have only been used to a limited extent. Infrared emission spectroscopy (IES) forms a valuable technique that can be applied in situ during the heat treatment. The IES technique removes the difficulties of heating the sample to temperatures where reactions take place with subsequent quenching prior to the measurement, because IES measures the process as it is actually taking place.