A new state-of-the-art balloon borne three channel (500, 625, 1800 GHz) cryogenic heterodyne spectrometer will allow enhanced limb sounding of the Earth's atmosphere within the submillimeter and far-infrared spectral range. The instrument, called TELIS (TErahertz and submm LImb Sounder), is being developed by a consortium of major European institutes that includes the Space Research Organisation of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) in the United Kingdom and the Deutschen Zentrum für Luft- und Raumfahrt (DLR) in Germany (lead institute). TELIS will utilise state-of-the-art super­conducting heterodyne technology and is designed to be compact and lightweight, while providing broad spectral coverage, high spectral resolution and long flight duration (~24 hours duration during a single flight campaign). The combination of high sensitivity and extensive flight duration will allow investigation of the diurnal variation of key atmospheric short-lived radicals such as OH, HO2, ClO, BrO together with stable constituents such as O3, HCl and HOCl. Furthermore, TELIS will share a balloon platform with the MIPAS-B Fourier transform spectrometer, developed by the Institute of Meteorology and Climate Research of the University of Karlsruhe, Germany. MIPAS-B will provide simultaneous and complementary spectral measurements over an extended spectral range. The combination of the TELIS and MIPAS instruments will provide atmospheric scientists with a very powerful observational tool and, in addition, will act as a prelude to future spaceborne instruments.