The observation of electromagnetic waves from the Universe at wavelengths of about 1–10 mm, a part of the spectrum rich in lines emitted by interstellar molecules. Millimetre-wave astronomy is one of the newest fields in astronomy and is used to study many processes, such as the chemistry of interstellar matter and the complex processes in star-forming regions and dark clouds. The cosmic microwave background is brightest in this part of the spectrum. Major millimetre-wave facilities include the Atacama Large Millimeter/submillimeter Array and the Institut de Radio Astronomie Millimétrique (IRAM). See also Submillimetre Astronomy.