Title: Wasserstein Distributionally Robust Optimization: A Three-Player Game Framework. Abstract: Wasserstein distributionally robust optimization (DRO) has recently received significant attention in machine learning due to its connection to generalization, robustness and regularization. Existing methods only consider a limited class of loss functions or apply to small values of robustness. In this paper, we present a three-player game framework for solving Wasserstein DRO problem with arbitrary level of robustness, which can handle general loss functions. Specifically, we formulate a min-max game between three players who optimize over probability measures, model parameters and Lagrange multipliers. We also propose new algorithms for finding an equilibrium of the game in convex and non-convex settings which both enjoy provable convergence guarantees. Furthermore, we prove an excess risk bound for the proposed algorithms which shows that the solution returned by the algorithms closely achieves the optimal minimax risk.  