  The Hubble Space Telescope has devoted 500 orbits to observing 250 massive
stars with low metallicity in the ultraviolet (UV) range within the framework
of the ULLYSES program. The X-Shooting ULLYSES (XShootU) project enhances the
legacy value of this UV dataset by providing high-quality optical and
near-infrared spectra, which are acquired using the wide-wavelength-coverage
X-shooter spectrograph at ESO's Very Large Telescope. XShootU emphasises the
importance of combining UV with optical spectra for the consistent
determination of key stellar parameters such as effective temperature, surface
gravity, luminosity, abundances, and wind characteristics including mass-loss
rates as a function of metallicity. Since uncertainties in these parameters
have implications across various branches of astrophysics, the data and
modelling generated by the XShootU project are poised to significantly advance
our understanding of massive stars at low metallicity. This is particularly
crucial for confidently interpreting JWST data of the earliest stellar
generations, making XShootU a unique resource for comprehending individual
spectra of low-metallicity stars.
