The Atacama B-mode Search (ABS) was a cryogenic crossed-Dragone telescope located at an elevation of 5200 m in the Atacama Desert in Chile that observed the cosmic microwave background (CMB) from February 2012 until October 2014. ABS was a pathfinder experiment that searched on degree-angular scales for inflationary B-modes in the CMB and pioneered the use of a rapidly-rotating half-wave plate (HWP), which modulates the polarization of incoming light to permit the measurement of celestial polarization on large angular scales that would otherwise be obscured by atmospheric noise. I will discuss the ABS telescope, describe novel instrument characterization techniques using the HWP, and give an overview of the first two seasons of ABS data.