Objective: The benefits of physical activity for executive functioning have been established across the lifespan but little is known about the role of sedentary behavior in these relations. This study evaluated the role of both physical activity and sedentary behavior in daily cognition and whether these relations are acute (i.e., based on within-person fluctuations in daily behavior), chronic (i.e., based on between-person differences in usual behavior), or both. Methods : A 14-day ecological momentary assessment study was conducted using daily diary and ambulatory monitoring methods with a college student sample. Results: Self-reported daily physical activity and sedentary behavior were positively and negatively associated, respectively, with daily deviations in perceived cognitive abilities. Accelerometer data indicated that Ddaily physical activity was positively associated with daily deviations in perceived cognitive abilities but daily sedentary behavior was not associated with daily cognitive abilities. Contrary to previous research, both self-reports and accelerometers indicated that people’s usual levels of physical activity and sedentary behaviors were not associated with their perceived cognitive abilities. Conclusions: Daily changes in physical activity appear to be associated with daily cognition. Further research is needed to establish the direction of causality and resolve the equivocal findings regarding sedentary behavior and daily cognitive abilities.