  We describe BOOMERANG; a balloon-borne microwave telescope designed to map
the Cosmic Microwave Background (CMB) at a resolution of 10' from the Long
Duration Balloon (LDB) platform. The millimeter-wave receiver employs new
technology in bolometers, readout electronics, cold re-imaging optics,
millimeter-wave filters, and cryogenics to obtain high sensitivity to CMB
anisotropy. Sixteen detectors observe in 4 spectral bands centered at 90, 150,
240 and 410 GHz. The wide frequency coverage, the long duration flight, the
optical design and the observing strategy provide strong rejection of
systematic effects. We report the flight performance of the instrument during a
10.5 day stratospheric balloon flight launched from McMurdo Station, Antarctica
that mapped ~2000 square degrees of the sky.
