This volume consists of invited lectures and seminars presented at the NATO Advanced Study Institute "The Infrared and Submillimetre Sky after COBE," which was held at the Centre de Physique Theorique of Les Houches (France) in March 1991. The school has been planned by a Scientific Organizing Committee. It was organized with the aim of providing students and young researchers with an up-to-date account of the Cosmic Microwave Background, the Cosmic Infrared Background (if any), and the infrared emission of the Galaxy, after the early results from COBE (Cosmic Background Explo rer). It was...