  We present the first public data release of the GOGREEN and GCLASS surveys of
galaxies in dense environments, spanning a redshift range $0.8<z<1.5$. The
surveys consist of deep, multiwavelength photometry and extensive Gemini GMOS
spectroscopy of galaxies in 26 overdense systems ranging in halo mass from
small groups to the most massive clusters. The objective of both projects was
primarily to understand how the evolution of galaxies is affected by their
environment, and to determine the physical processes that lead to the quenching
of star formation. There was an emphasis on obtaining unbiased spectroscopy
over a wide stellar mass range ($M\gtrsim 2\times 10^{10}~\mathrm{M}_\odot$),
throughout and beyond the cluster virialized regions. The final spectroscopic
sample includes 2771 unique objects, of which 2257 have reliable spectroscopic
redshifts. Of these, 1704 have redshifts in the range $0.8<z<1.5$, and nearly
800 are confirmed cluster members. Imaging spans the full optical and
near-infrared wavelength range, at depths comparable to the UltraVISTA survey,
and includes \textit{HST}/WFC3 F160W (GOGREEN) and F140W (GCLASS). This data
release includes fully reduced images and spectra, with catalogues of advanced
data products including redshifts, line strengths, star formation rates,
stellar masses and rest-frame colours. Here we present an overview of the data,
including an analysis of the spectroscopic completeness and redshift quality.
