The Laboratory (full official name is Microwave Spectroscopy Division) was organized in 1977, with the organization of IAP RAS. The division was grown on the base of works of the group of A.F. Krupnov in NIRFI which led to developments of submillimeter wave spectrometer with Backward Wave Oscillators (BWO's) and acoustic detection (RAD) and the phase lock-in system of submillimeter BWO's (both in 1970). Both these developments appeared to be very successful and gave good perspective for many further developments of submillimeter wave spectroscopic technique and investigations of molecular spectra (see Instruments and List of publications). Division of microwave spectroscopy first in the new Institute got the State Prize of USSR in Science (1980, "For Development of Submillimeter Wave Spectroscopy with Backward Wave Oscillators"). Current activity of the Laboratory is presented on the site. A.F. Krupnov headed the Division since 1977 to 2005; at the present time Head of the Division is M.Yu. Tretyakov.