Hot-star models from 100 to 10,000 Å

The spectral libraries of hot, massive stars which are implemented in the population synthesis code Starburst99 are discussed. Hot stars pose particular challenges for generating libraries. They are rare, they have an intense radiation field and strong stellar winds, and a luminosity bias towards ultraviolet wavelengths. These properties require the utilization of theoretical libraries. Starburst99 uses static non-LTE models at 0.3 Å resolution in the optical, spherically extended, expanding models at 0.4 Å resolution, in the satellite-ultraviolet, and blanketed, low-resolution radiation-hydrodynamical models in the extreme ultraviolet down to X-rays. I review the main features of each library, compare them to observations, and discuss their link with stellar evolution models.