This thesis describes a new balloon-borne system which was designed, constructed, and flown with the purpose of increasing the sensitivity of gamma-ray observations. In an attempt to reduce the background counting rate, the detector employed a previously-untried composite shield of the following materials and depths of materials (in units of gm cm-2): plastic scintillator - 4, LiF epoxy - 2, lead - 43, sodium iodide - 5, and aluminum - 7. Both the plastic and the Nal (Tl) scintillators were used in an active anticoincidence system; the plastic detects charged particles which may initiate cascades in the lead collimator, and the sodium iodide detects low energy photons which emerge from the inner surface of the lead. The LiF epoxy is a slow neutron absorber, and the aluminum was used as the supporting structure. The new telescope system is capable of remaining aloft for ~40 hours and, through radio-control, of observing several celestial objects during a given flight. The detector proved to be a very effective collimator of gamma rays and exhibited a low counting rate at sea level. The high counting rate that was encountered at balloon altitudes, though unexpected, can, however, be explained in terms of Compton and neutron interactions in the central crystal which was composed of CsI (Na).