  We introduce the Ophiuchus DIsc Survey Employing ALMA (ODISEA), a project
aiming to study the entire population of Spitzer-selected protoplanetary discs
in the Ophiuchus Molecular Cloud (~300 objects) from both millimeter continuum
and CO isotopologues data. Here we present 1.3 mm/230 GHz continuum images of
147 targets at 0.2" (28 au) resolution and a typical rms of 0.15 mJy. We detect
a total of 133 discs, including the individual components of 11 binary systems
and 1 triple system. Fifty-three of these discs are spatially resolved. We find
clear substructures (inner cavities, rings, gaps, and/or spiral arms) in 8 of
the sources and hints of such structures in another 4 discs. We construct the
disc luminosity function for our targets and perform comparisons to other
regions. A simple conversion between flux and dust mass (adopting standard
assumptions) indicates that all discs detected at 1.3 mm are massive enough to
form one or more rocky planets. In contrast, only ~50 discs (~1/3 of the
sample) have enough mass in the form of dust to form the canonical 10 M_Earth
core needed to trigger runaway gas accretion and the formation of gas giant
planets, although the total mass of solids already incorporated into bodies
larger than cm scales is mostly unconstrained. The distribution in continuum
disc sizes in our sample is heavily weighted towards compact discs: most
detected discs have radii < 15 au, while only 23 discs (~15% of the targets)
have radii > 30 au.
