In this paper, we propose a duality theory for semi-in…nite linear programming problems under uncertainty in the constraint functions, the objective function, or both, within the framework of robust optimization. We present robust duality by establishing strong duality between the robust counterpart of an uncertain semi-in…nite linear program and the optimistic counterpart of its uncertain Lagrangian dual. We show that robust duality holds whenever a robust moment cone is closed and convex. We then show that the closed-convex robust moment cone condition in the case of constraint-wise uncertainty is in fact necessary and su¢ cient for robust duality in the sense that robust moment cone is closed and convex if and only if robust duality holds for every linear objective function of the program. In the case of uncertain problems with a¢ nely parameterized data uncertainty, we establish that robust duality is easily satis…ed under a Slater type constraint quali…cation. Consequently, we derive robust forms of the Farkas lemma for systems of uncertain semi-in…nite linear inequalities.