I will briefly describe the Gaia mission capabilities, science goals, and status. I will then focus on the open problems in the study of Galactic globular clusters (GC) and their relation with the Galactic halo, like the contribution of stars lost by GC to the assembly of the halo; the search for streams, tails, and debris from GC; the two channels of formation, in situ and accreted; and the mystery of multiple stellar populations. I will then discuss the amazing contribution that Gaia can provide to answer these questions, both alone and in conjunction with ongoing and planned ground-based surveys, with special attention to its often underevaluated crowded stellar field capabilities.