Since 2006, we started assembling a grid of spectrophotometric standard stars (SPSS), calibrated on the HST CALSPEC system, to calibrate Gaia spectro-photometry with an accuracy of 1% or better. We used a variety of small and medium size telescope for a total of about 500 nights and we succeeded in reaching what is commonly accepted as the limiting accuracy in current technology. The grid covers a variety of spectral types, which is necessary to accurately calibrate the Gaia data, and the flux tables cover the wavelength range of Gaia (300-1200 nm). The project is almost completed and we are now working on the final release of flux tables. 

As a spinoff of our work on the calibration of Gaia photometry, we prepared a curated version of all the Landolt and Stetson catalogs of primary and secondary photometry standard stars for the Johnson-Kron-Cousins UBVRI photometric system. We used the full power of Gaia and large surveys to prune out less reliable stars and to characterize the stars in terms of stellar parameters. We also provide updated transformations between the UBVRI system and several of the most widely used photometric systems.