  We describe a deep, systematic imaging study of satellites in the outer halo
of the Milky Way. Our sample consists of 58 stellar overdensities --- i.e.,
substructures classified as either globular clusters, classical dwarf galaxies,
or ultra-faint dwarf galaxies --- that are located at Galactocentric distances
of R$_{\rm GC}$ > 25 kpc (outer halo) and out to ~400 kpc. This includes 44
objects for which we have acquired deep, wide-field, $g-$ and $r-$band imaging
with the MegaCam mosaic cameras on the 3.6m Canada-France-Hawaii Telescope and
the 6.5m Magellan-Clay telescope. These data are supplemented by archival
imaging, or published $gr$ photometry, for an additional 14 objects, most of
which were discovered recently in the Dark Energy Survey (DES). We describe the
scientific motivation for our survey, including sample selection, observing
strategy, data reduction pipeline, calibration procedures, and the depth and
precision of the photometry. The typical 5$\sigma$ point-source limiting
magnitudes for our MegaCam imaging --- which collectively covers an area of ~52
deg$^{2}$ --- are $g_{\rm lim}$ ~25.6 and $r_{\rm lim}$ ~25.3 AB mag. These
limits are comparable to those from the coadded DES images and are roughly a
half-magnitude deeper than will be reached in a single visit with LSST. Our
photometric catalog thus provides the deepest and most uniform photometric
database of Milky Way satellites available for the foreseeable future. In other
papers in this series, we have used these data to explore the blue straggler
populations in these objects, their density distributions, star formation
histories, scaling relations and possible foreground structures.
