Appears in collection : 100 (102!) Years of the Ising Model

In its modern incarnation (developed during the last two decades), Ornstein-Zernike theory enables a non-perturbative analysis of non-critical ferromagnetic Ising models (and other models). I'll review some of its recent applications to the asymptotics of correlation functions (in any dimension) and to the fluctuation theory of interfaces (in the planar model).