Spectroscopy of asteroids can be diagnostic of their surface composition and other properties such as internal structure. The European Space Agency's Gaia mission will result in a dramatic increase in the number and quality of asteroid spectra in the 0.35–0.9 μm wavelength range. This homogeneous set of spectra, with high sensitivity in the near-ultraviolet, will be of great benefit to the study of asteroids. In this work, we focus on Gaia's expected contributions to the understanding of asteroids families and we use the Themis family as an example. Spectra of main belt asteroids as small as 2 km in diameter will constrain or determine the composition and thermal evolution of a family's parent body. In the case of the Themis family, Gaia's spectra will also help establish the role of water and hydrated minerals in the evolution of this family, including the puzzling nature of the “main belt comets” or “activated asteroids” within this family.