  Surveys in the Milky Way and Large Magellanic Cloud revealed that the
majority of massive stars will interact with companions during their lives.
However, knowledge of the binary properties of massive stars at low
metallicity, which approaches the conditions of the Early Universe, remains
sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign - an ESO
large programme designed to obtain 25 epochs of spectroscopy for 929 massive
stars in the SMC - the lowest metallicity conditions in which multiplicity is
probed to date (Z = 0.2 Zsun). BLOeM will provide (i) the binary fraction, (ii)
the orbital configurations of systems with periods P < 3 yr, (iii) dormant
OB+BH binaries, and (iv) a legacy database of physical parameters of massive
stars at low metallicity.
  The stars are observed with the LR02 setup of the giraffe instrument of the
Very Large Telescope (3960-4570A, resolving power R=6200; typical
signal-to-noise ratio S/N=70-100). This paper utilises the first 9 epochs
obtained over a three-month time. We describe the survey and data reduction,
perform a spectral classification of the stacked spectra, and construct a
Hertzsprung-Russell diagram of the sample via spectral-type and photometric
calibrations. The sample covers spectral types from O4 to F5, spanning the
effective temperature and luminosity ranges 6.5<Teff/kK<45 and 3.7<log
L/Lsun<6.1 and initial masses 8<Mini/Msun<80. It comprises 159 O-type stars,
324 early B-type (B0-3) dwarfs and giants (luminosity classes V-III), 309 early
B-type supergiants (II-I), and 137 late-type supergiants. At least 75 stars are
Oe/Be stars: 20 O-type and 55 B-type (13% and 10% of the respective samples).
In addition, it includes four high-mass X-ray binaries, three stars resembling
luminous blue variables, two bloated stripped-star candidates, two candidate
magnetic stars, and 74 eclipsing binaries.
