  The Atacama B-mode Search (ABS) is an experiment designed to measure cosmic
microwave background (CMB) polarization at large angular scales ($\ell>40$). It
operated from the ACT site at 5190~m elevation in northern Chile at 145 GHz
with a net sensitivity (NEQ) of 41 $\mu$K$\sqrt{\rm s}$. It employed an
ambient-temperature sapphire half-wave plate rotating at 2.55 Hz to modulate
the incident polarization signal and reduce systematic effects. We report here
on the analysis of data from a 2400 deg$^2$ patch of sky centered at
declination $-42^\circ$ and right ascension $25^\circ$. We perform a blind
analysis. After unblinding, we find agreement with the Planck TE and EE
measurements on the same region of sky. We marginally detect polarized dust
emission and give an upper limit on the tensor-to-scalar ratio of $r<2.3$ (95%
cl) with the equivalent of 100 on-sky days of observation. We also present a
new measurement of the polarization of Tau A and introduce new methods
associated with HWP-based observations.
