The death of a star is a complex process that plays a key role in the chemical evolution of the Universe, particularly in the formation of dust grains. At the end of their lives, Sun-like stars undergo an intense mass-loss process that creates a surrounding circumstellar envelope (CSE) composed mainly of molecular gas and dust. Eventually, all this material enriches the interstellar medium, the base component for later cloud, stellar, and planetary formation. After decades of research and observations, the physical conditions in these objects, which span the properties of a variety of different astrophysical environments, are relatively well-known. They thus present one of the best astronomical laboratories in which to investigate the formation and destruction of molecules and dust and the growth of molecular complexity.