Polymorphism of drug compounds is a critical issue within the pharmaceutical industry. Vibrational spectroscopy techniques play an important and ever increasing role in the identification, analysis and characterization of different forms, both crystalline and amorphous, of pharmaceutical drug substances. This chapter discusses the role, advantages, some applications, and limitations of mid‐, near‐ and far‐infrared, terahertz and Raman spectroscopy to the characterization, both qualitative and quantitative, of polymorphs, solvates and hydrates. It outlines the principles behind the effects polymorphism may have on a vibrational spectrum, and exemplifies the complementary requirement for applying a range of analytical techniques to each polymorphism study. For each vibrational spectroscopy technique discussed, consideration is given to sampling, and to qualitative, both macro‐ and micro‐, and quantitative applications.