Stellar spectroscopy is the technique to determine stellar parameters and chemical abundances of stars, and relies on the modeling of stellar atmospheres which are based on simplistic (therefore uncertain) assumptions. The Gaia Benchmark Stars are well-known stars from which information about their structure beyond the spectra can be obtained (interferometric and astrometric measurements). These stars have become the calibration pillars for Gaia and for its complementary spectroscopic surveys. At UDP we assemble them, observe them, perform high resolution spectroscopy, and assess the quality of lines in both the optical and the infrared spectral range.
