This document discusses the intrinsic robustness of the price of anarchy concept in game theory. It defines key concepts like pure Nash equilibrium, price of anarchy, and smooth games. Smooth games are games where the cost of any outcome is close to the cost of the optimal outcome. The document proves several games are smooth, including congestion games with affine costs, valid utility games, and simultaneous second-price auctions. It introduces the concept of robust price of anarchy as being defined based on the smoothness parameters of a game. The document also presents an extension theorem showing price of anarchy bounds extend beyond pure Nash equilibrium to other equilibrium concepts and outcome sequences.