provide a useful summary of all but the most recent work. Among the chemically peculiar stars with [\[Fe/H\]]{} $\leq -2.0$, objects with enhanced carbon abundance are the most common variety.

The carbon-enhancement phenomenon was recognized over a half century ago for stars with \[Fe/H\] $\sim$ –2.0 to \[Fe/H\] $\sim -1.0$. Such objects were called CH stars (Keenan 1942) or subgiant CH stars (Bond 1974), because their optical spectra exhibit strong CH $G$-band absorption features around 4300 Å compared to stars with similar effective temperatures and metallicities. Over the past quarter century, spectroscopic follow-up of metal-poor candidates selected from the HK and HES surveys have identified many more such stars at even lower metallicity (e.g., Beers et al. 1985, 1992; Christlieb et al. 2001; Christlieb 2003). These stars are referred to as carbon-enhanced metal-poor (CEMP) stars, originally defined as having metallicity \[Fe/H\] $\leq -1.0$ and carbon-to-iron ratios larger than 10 times the solar ratio (i.e., \[C/Fe\] $> +1.0$; Beers & Christlieb 2005); definitions of CEMP stars using the criteria \[C/Fe\] $> +0.5$ and \[C/Fe\] $> +0.7$ have also been employed by a number of authors (e.g., Aoki et al. 2007).

Recent studies of VMP stars discovered from various spectroscopic surveys have 