  The Dark Energy Spectroscopic Instrument (DESI) will precisely constrain
cosmic expansion and the growth of structure by collecting $\sim$40 million
extra-galactic redshifts across $\sim$80\% of cosmic history and one third of
the sky. The Emission Line Galaxy (ELG) sample, which will comprise about
one-third of all DESI tracers, will be used to probe the Universe over the $0.6
< z < 1.6$ range, which includes the $1.1<z<1.6$ range, expected to provide the
tightest constraints.
  We present the target selection of the DESI SV1 Survey Validation and Main
Survey ELG samples, which relies on the Legacy Surveys imaging. The Main ELG
selection consists of a $g$-band magnitude cut and a $(g-r)$ vs.\ $(r-z)$ color
box, while the SV1 selection explores extensions of the Main selection
boundaries.
  The Main ELG sample is composed of two disjoint subsamples, which have target
densities of about 1940 deg$^{-2}$ and 460 deg$^{-2}$, respectively. We first
characterize their photometric properties and density variations across the
footprint. Then we analyze the DESI spectroscopic data obtained since December
2020 during the Survey Validation and the Main Survey up to December 2021. We
establish a preliminary criterion to select reliable redshifts, based on the
\oii~flux measurement, and assess its performance. Using that criterion, we are
able to present the spectroscopic efficiency of the Main ELG selection, along
with its redshift distribution. We thus demonstrate that the the main selection
with higher target density sample should provide more than 400 deg$^{-2}$
reliable redshifts in both the $0.6<z<1.1$ and the $1.1<z<1.6$ ranges.
