I will discuss the Maldacena-Lewkowycz derivation of the Ryu-Takayangi prescrition for holographic entanglement entropy, and extend it to a more general class of theories of gravity in the bulk. This analysis results in a new euclidean entropy functional, that generalises Wald's entropy. In lorentzian signature, this functional is a natural extension of Wald's black hole entropy to time dependent situations.