the Sloan Digital Sky Survey (SDSS; Fukugita et al. 1996; Gunn et al. 1998, 2006; York et al. 2000; Stoughton et al. 2002; Abazajian et al. 2003, 2004, 2005, 2009; Pier et al. 2003; Adelman-McCarthy et al. 2006, 2007, 2008; Aihara et al. 2011; Ahn et al. 2012) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE-1; Yanny et al. 2009) and SEGUE-2 (C. Rockosi et al., in preparation), to many tens of thousands of VMP stars. Ongoing surveys, such as Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST; Cui et al. 2012; Luo et al. 2012), hold the promise of enlarging this sample to several hundred thousand VMP stars.

Detailed chemical-abundance analyses by a number of groups, based on high-resolution spectroscopic follow-up, have revealed that, while most VMP stars exhibit similar abundance patterns, there are numerous examples of objects with peculiar chemical patterns, such as strong enrichments or deficiencies of light elements such as C, N, O, Na, Mg, Si, etc. (e.g., McWilliam et al. 1995; Ryan et al. 1996; Norris et al. 2001, 2013; Johnson 2002; Cayrel et al. 2004; Aoki et al. 2008, 2013; Cohen et al. 2008; Lai et al. 2008). Frebel & Norris (2012) 