Published online by Cambridge University Press: 26 February 2009
IR spectroscopy is the premier tool to study the composition of interstellar dust. Broad absorption and emission bands provide direct identification of the solid compounds present in space and allow measurement of accurate abundances. Systematic studies of large samples of sources allow then inferences on the origin and evolution of dust in space. Overall, the observed infrared spectra of interstellar and circumstellar dust reveals an incredibly rich and varied composition. This chapter briefly reviews the principles of infrared spectroscopy. This is then applied to the composition of circumstellar oxides and minerals and interstellar Polycyclic Aromatic Hydrocarbon molecules.