The simplest toy models for classical and quantum gravity that can have black hole solutions are two-dimensional. Yet, two-dimensional Einstein gravity is not among them: in two dimensions the Einstein tensor vanishes identically. Nevertheless, a family of consistent theories of gravity is provided by two-dimensional dilaton gravity. Holography in these models, however, appears to be more subtle than its higher-dimensional relative; only recently a possible boundary theory for dilaton gravity in AdS_2 was proposed in the form of the Sachdev-Ye-Kitaev model. Following an introduction to two-dimensional dilaton gravity and its reformulation as a gauge theory I will describe the holographic renormalization of various dilaton gravity models and discuss possible set-ups for holography in AdS_2.