Stress can affect cognition in many ways, with the outcome (i.e., facilitating or impairing) depending on a combination of factors related to both stress and the cognitive function under study. Among the factors identified as particularly relevant to define the cognitive effects of stress are the intensity or magnitude of stress, its origin (i.e., whether triggered by the task or externally), and its duration (i.e., whether acute or chronically delivered). At the cognitive end, the specific cognitive operation (e.g., implicit or explicit memory, long-term or working memory, goal-directed or habit learning) and information processing phases (e.g., learning, consolidation, and retrieval) are essential as well to define stress effects. The emerging view is that mild stress tends to facilitate cognitive function, particularly in implicit memory or simple declarative tasks or when the cognitive load is not excessive. Exposure to high or very high stress acutely (whether elicited by the cognitive task or experienced before being trained or tested in the task) or chronically impairs the formation of explicit memories and, more generally, of those that require complex, flexible reasoning (as typically observed for hippocampus- and prefrontal cortex-related functions) while improving performance of implicit memory and well-rehearsed tasks (as reported for amygdala-dependent conditioning tasks and for striatum-related processes). In addition to these general principles, there are important individual differences in the cognitive impact of stress, with gender and age being particularly influencing factors. WIREs Cogn Sci 2013, 4:245261. doi: 10.1002/wcs.1222 For further resources related to this article, please visit the WIREs website.