The abundances of elements in the protoplanetary disk evolve over time, but stellar abundances will reflect the initial chemical composition of the disk and this can provide constraints on the range of possible outcomes for
planet interiors. In this talk I will discuss the C/O and Mg/Si ratios of stars in the solar neighborhood and how that could affect the habitability of any rocky planets around them. The slow evolution of abundances in stellar photospheres, particularly abundance ratios between elements, makes
them ideal laboratories to study primordial disk compositions. As we begin to dedicate scarce telescope time to the search for Earth 2.0, composition will be an important tool in determining which of the many Earth-sized planets are truly Earth-like.
Our recently published catalog of accurate stellar parameters and precise abundances of 15 elements for more than 1600 stars can also be used investigate other questions of planet formation. For lucky cases where planet atmospheric abundances can be measured, the stellar host C/O and [O/H] ratios carries information about the formation site and migration of hot Jupiters.