  We present the PRIsm MUlti-object Survey (PRIMUS), a spectroscopic faint
galaxy redshift survey to z~1. PRIMUS uses a low-dispersion prism and slitmasks
to observe ~2,500 objects at once in a 0.18 deg^2 field of view, using the
IMACS camera on the Magellan I Baade 6.5m telescope at Las Campanas
Observatory. PRIMUS covers a total of 9.1 deg^2 of sky to a depth of i_AB~23.5
in seven different deep, multi-wavelength fields that have coverage from GALEX,
Spitzer and either XMM or Chandra, as well as multiple-band optical and near-IR
coverage. PRIMUS includes ~130,000 robust redshifts of unique objects with a
redshift precision of dz/(1+z)~0.005. The redshift distribution peaks at z=0.6
and extends to z=1.2 for galaxies and z=5 for broad-line AGN. The motivation,
observational techniques, fields, target selection, slitmask design, and
observations are presented here, with a brief summary of the redshift
precision; a companion paper presents the data reduction, redshift fitting,
redshift confidence, and survey completeness. PRIMUS is the largest faint
galaxy survey undertaken to date. The high targeting fraction (~80%) and large
survey size will allow for precise measures of galaxy properties and
large-scale structure to z~1.
