Quantum correlations in general and quantum entanglement in particular embody both our continued struggle towards a foundational understanding of quantum theory as well as the latter's advantage over classical physics in various information processing tasks. Consequently, the problems of classifying (i) quantum states from more general (non-signalling) correlations, and (ii) entangled states within the set of all quantum states, are at the heart of the subject of quantum information theory. In this talk I will present two recent results (
) that shed new light on these problems, by exploiting a surprising connection with time in quantum theory: First, I will sketch a solution to problem (i) for the bipartite case, which identifies a key physical principle obeyed by quantum theory: quantum states preserve time orientations—roughly, the unitary evolution in local subsystems. Second, I will show that time orientations are intimately connected with quantum entanglement: a bipartite quantum state is separable if and only if it preserves arbitrary time orientations. As a variant of Peres's well-known entanglement criterion, this provides a solution to problem (ii).