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One pathway by which environments of socioeconomic risk are thought to affect cognitive development is through stress physiology. The biological systems underpinning stress and attention undergo a sensitive period of development during infancy. Psychobiological theory emphasizes a dynamic pattern of context-dependent development, however, research has yet to examine how basal cortisol and attention dynamically covary across infancy in ecologically valid contexts. Thus, to address these gaps, we leveraged longitudinal, multilevel analytic methods to disentangle between- from within-person associations of hypothalamic–pituitary–adrenal (HPA) axis activity and executive attention behaviors across infancy. We use data from a large longitudinal sample (N = 1,292) of infants in predominantly low-income, nonurban communities at 7-, 15-, and 24-months of age. Using multilevel models, we investigated longitudinal associations of infant attention and basal cortisol levels and examined caregiving behaviors as moderators of this relationship. Results indicated a negative between- and within-person association between attention and cortisol across infancy and a within-person moderation by caregiver responsiveness. In other words, on the within-person level, higher levels of cortisol were concomitantly associated with lower infant attention across the first 2 years of life. However, variation in the caregiver's level of responsiveness either buffered or sensitized the executive attention system to the negative effects of physiological stress. [ABSTRACT FROM AUTHOR]