  The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct
novel cosmological observations using the BOSS spectrograph at Apache Point
Observatory. Observations will be simultaneous with the Time Domain
Spectroscopic Survey (TDSS) designed for variability studies and the
Spectroscopic Identification of eROSITA Sources (SPIDERS) program designed for
studies of X-ray sources. eBOSS will use four different tracers to measure the
distance-redshift relation with baryon acoustic oscillations (BAO). Using more
than 250,000 new, spectroscopically confirmed luminous red galaxies at a median
redshift z=0.72, we project that eBOSS will yield measurements of $d_A(z)$ to
an accuracy of 1.2% and measurements of H(z) to 2.1% when combined with the
z>0.6 sample of BOSS galaxies. With ~195,000 new emission line galaxy
redshifts, we expect BAO measurements of $d_A(z)$ to an accuracy of 3.1% and
H(z) to 4.7% at an effective redshift of z= 0.87. A sample of more than 500,000
spectroscopically-confirmed quasars will provide the first BAO distance
measurements over the redshift range 0.9<z<2.2, with expected precision of 2.8%
and 4.2% on $d_A(z)$ and H(z), respectively. Finally, with 60,000 new quasars
and re-observation of 60,000 quasars known from BOSS, we will obtain new
Lyman-alpha forest measurements at redshifts z>2.1; these new data will enhance
the precision of $d_A(z)$ and H(z) by a factor of 1.44 relative to BOSS.
Furthermore, eBOSS will provide improved tests of General Relativity on
cosmological scales through redshift-space distortion measurements, improved
tests for non-Gaussianity in the primordial density field, and new constraints
on the summed mass of all neutrino species. Here, we provide an overview of the
cosmological goals, spectroscopic target sample, demonstration of spectral
quality from early data, and projected cosmological constraints from eBOSS.
