Classical spin-glass models such as Sherrington-Kirkpatrick's are paradigms for complex disordered systems. In 1980, Parisi described their thermodynamic behaviour using a novel order parameter that captures the emergent hierarchical spin-glass order at low temperatures. The fate of this low-temperature phase with respect to quantum effects induced, e.g., by a transverse magnetic field is a fundamental question. In this talk, I will report on recent progress in the mathematical description of such quantum glasses. In particular, I will describe what a quantum version of Parisi's famous variational formula looks like.