Development does not take place in isolation; close others form an important dyad for exploring interrelationships. To examine spousal interrelations in level and change of cognitive functioning in old age, the authors applied dynamic models to 11-year longitudinal data of, initially, 304 married couples from the Australian Longitudinal Study of Ageing (aged 64-98 years at Time 1; M = 76 years). Findings revealed that perceptual speed for husbands predicted subsequent perceptual speed decline for wives (time lags of 1 year). There was little evidence for the opposite unidirectional effect or a bidirectional association between husbands and wives. Potential covariates (age, education, medical conditions, functional limitations, and depressive symptoms) did not account for differential lead-lag associations. A similar, though less pronounced, pattern was found for memory, which held except when functional limitations were controlled. Findings suggest that late-life cognitive development is not solely a product of intraindividual resources and are consistent with conceptual notions that development actively influences, and is influenced by, contextual factors such as close relationships. The authors discuss possible underlying mechanisms and further steps to substantiate the findings.