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In the well-studied agnostic model of learning, the goal of a learner– given examples from an arbitrary joint distribution on Rd ⇥ {±1}– is to output a hypothesis that is competitive (to within ✏) of the best fitting concept from some class. In order to escape strong hardness results for learning even simple concept classes in this model, we introduce a smoothed analysis framework where we require a learner to compete only with the best classifier that is robust to small random Gaussian perturbation. This subtle change allows us to give a wide array of learning results for any concept that (1) depends on a low-dimensional subspace (aka multi-index model) and (2) has a bounded Gaussian surface area. This class includes functions of halfspaces and (low-dimensional) convex sets, cases that are only known to be learnable in non-smoothed settings with respect to highly structured distributions such as Gaussians. Perhaps surprisingly, our analysis also yields new results for traditional non-smoothed frame- works such as learning with margin. In particular, we obtain the first algorithm for agnostically learning intersections of k-halfspaces in time kpoly( log k ✏ ) where is the margin parameter. Before our work, the best-known runtime was exponential in k (Arriaga and Vempala, 1999a).