Robustness is the ability of a system to maintain its function despite perturbation. To function in an unpredictable environment using unreliable components, a system must be robust. Robustness is fundamental to biological systems (Kitano, 2004) and is an objective in the design of engineered artifacts such as airplane engines (Reinman et al., 2012) and buildings (Starossek & Haberland, 2012). The cognitive system, like biological and engineered systems, exists within a variable environment. In this work, we extend the formality that exists in the study of biological and engineered robustness to the study of cognitive robustness. We illustrate our approach with two applications: the first reveals mechanisms that enhance the robustness of the cognitive system against fatigue, and the second provides insight into the robustness of a class of decision heuristics.