MIPAS-B2 is a cryogenic limb-sounder dedicated to stratospheric trace gas research. The balloon borne instrument is a precursor of the MIPAS instrument on the ESA ENVISAT satellite. In consequence, the main instrumental specifications and parameters are similar. The instrument has been flown several times successfully in the frame of European atmospheric research campaigns (SESAME and THESEO) and a satellite validation campaign (ILAS). The heart of the instrument is a Fourier spectrometer working in the mid- infrared range (4 to 14 micrometer), which is cooled before launch to its operating temperature of 210 K with solid carbon dioxide. The spectral coverage is split into four spectral channels to improve sensitivity in particular in the short wavelength region. We employ liquid helium cooled Si:As-BIB- detectors to achieve optimum detectivity. A further important part of the instrument is the line of sight (LOS) stabilization system, which is based on an inertial navigation system and can be cross-examined with the help of an additional star reference system. The instrument was flown eight times from balloon launch sites in Sweden and France. The recorded data allowed the retrieval of many trace gases. One major scientific advantage of the instrument is the simultaneous detection of whole trace gas families in the stratosphere. All relevant night-time NOy species (NO2, N2O5, HNO3, ClONO2 and HO2NO2) together with the source gas N2O were successfully analyzed.