Impact of and relevance to Gaia

The Gaia mission, launched 19 December 2013, is key to answering many of these questions. It will provide photometry and astrometry of unprecedented precision for most stars brighter than around V=20, and obtain low-resolution spectra for most stars brighter than around V=16. The first astrometry data release will be in late summer 2016 for preliminary data, with spectrophotometry and first stellar parameters to follow in subsequent years, with the full catalogue anticipated around 2022. While Gaia is remarkable, like all spacecraft it leaves for large ground-based telescopes what those do best. That is the spectroscopy we propose here. The Gaia-ESO spectroscopy complements and completes Gaia astrometry, and vice versa. Each project is intrinsically exciting, and each benefits from synergy with the other.