The field of Molecular Astrophysics or “Astrochemistry” has grown considerably since its inception in the late 1930’s. Molecules have been observed in astronomical environments as diverse as comets in the solar system and galaxies at the highest redshifts. The common thread in these studies is that molecules are excellent probes of the physical structure and dynamics of such regions, owing to the complexity of their energy level structure and the resulting emission and absorption spectra. In addition, the chemical characteristics provide a powerful tool to study the evolution of astrophysical regions. Molecules also play an active role in the energy balance of clouds. Interstellar space is a unique laboratory in which chemical processes can occur that are not normally found on Earth. Indeed, astrochemistry is a highly interdisciplinary subject, linking the macrocosm (galaxies, stars, planets) with the microcosm (basic chemical processes and spectroscopy). The increased potential of ground- and space-based observational facilities over the full wavelength range provides a wealth of information about the physical environments in which molecules occur and makes it possible to study the development of molecular complexity throughout the Universe.