Smooth Kähler-Einstein metrics have been studied for the past 80 years. More recently, singular Kähler-Einstein metrics have emerged as objects of intrinsic interest, both in differential and algebraic geometry, as well as a powerful tool in better understanding their smooth counterparts. This article is mostly a survey of some of these developments.The Kähler-Einstein (KE) equation is among the oldest fully nonlinear equations in modern geometry. A wide array of tools have been developed or applied towards its understanding, ranging from Riemannian geometry, PDE, pluripotential theory, several complex variables, microlocal analysis, algebraic geometry, probability, convex analysis, and more. The interested reader is referred to the numerous existing surveys on related topics