Infrared spectroscopy involves the absorption of infrared radiation by molecules. There are two types of molecular vibrations that can occur upon absorption: molecular rotations below 100 cm-1 and molecular vibrations between 100-10,000 cm-1. Infrared spectroscopy provides information about the types of bonds in a molecule from their distinct absorption frequencies. It can be used to identify unknown molecules based on their unique infrared absorption fingerprint. Fourier transform infrared spectroscopy is now the most widely used technique as it acquires interferograms faster than dispersive infrared spectrometers. Infrared spectroscopy has applications in fields like pharmaceutical analysis, polymer characterization, and art conservation.