The production of a pair of isolated highly energetic photons in proton-proton collisions represents an important class of processes for the physics programme at the LHC and at future hadron colliders. Given the target accuracy, the theoretical description of the production of a pair of photons with large transverse momentum calls for the computation of higher-order corrections, and the next-to-next-to-leading (NNLO) QCD ones are at the current frontier.