Conway's NO is a class of numbers, originally thought as games, equipped with a natural ordered field structure and an exponential function which make it into a monster model of the theory of (R,exp). In a joint work with Berarducci, we determine the transseries structure of No, and we prove the existence of a natural differential field structure on No similar to the one of Hardy fields. It also turns out that the natural derivation is Liouville-closed, namely, it is surjective.