  (Abridged) Studying continuum emission from interstellar dust is essential to
locating and characterizing the highest density regions in the interstellar
medium. In particular, the early stages of massive star formation remain poorly
understood. Our goal is to produce a large-scale, systematic database of
massive pre- and proto-stellar clumps in the Galaxy, to understand how and
under what conditions star formation takes place. A well characterized sample
of star-forming sites will deliver an evolutionary sequence and a mass function
of high-mass, star-forming clumps. This systematic survey at submm wavelengths
also represents a preparatory work for Herschel and ALMA. The APEX telescope is
ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera
(LABOCA) is a 295-element bolometer array observing at 870 microns, with a beam
size of 19". Taking advantage of its large field of view (11.4') and excellent
sensitivity, we started an unbiased survey of the Galactic Plane, with a noise
level of 50-70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy
(ATLASGAL). As a first step, we covered 95 sq. deg. These data reveal 6000
compact sources brighter than 0.25 Jy, as well as extended structures, many of
them filamentary. About two thirds of the compact sources have no bright
infrared counterpart, and some of them are likely to correspond to the
precursors of (high-mass) proto-stars or proto-clusters. Other compact sources
harbor hot cores, compact HII regions or young embedded clusters. Assuming a
typical distance of 5 kpc, most sources are clumps smaller than 1 pc with
masses from a few 10 to a few 100 M_sun. In this introductory paper, we show
preliminary results from these ongoing observations, and discuss the
perspectives of the survey.
