Ornstein-Zernike theory for finite range Ising models above (T)c

We derive a precise Ornstein-Zernike asymptotic formula for the decay of the two-point function (sigma)(0)(sigma)(x) (beta)in the general context of finite range Ising type models on Ed. The proof relies in an essential way on the a-priori knowledge of the strict exponential decay of the two-point function and, by the sharp characterization of phase transition due to Aizenman, Barsky and Fern?ndez, goes through in the whole of the high temperature region (beta)<(beta)c. As a byproduct we obtain that for every (beta)<(beta)c, the inverse correlation length (zeta) is an analytic and strictly convex function of direction.