We examined associations between structural and functional aspects of social health, and subsequent trajectories of cognitive capability (memory, executive functioning, and processing speed).Using data from 16,858 participants (mean age 65.8 years; 56% female) from the National Survey for Health and Development (NSHD), the English Longitudinal Study of Aging (ELSA), the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), and the Rotterdam Study, we applied multilevel models to examine social health in relation to cognitive capability and the rate of cognitive decline.Those who were married/cohabiting scored 0.07SD (95%CI:0.00,0.14; heterogeneity I2=79%) higher on executive functioning compared to those who lived alone. Associations with memory and processing speed were also heterogeneous (I2>75%); for example, being married was associated with better memory in ELSA (0.05SD 95%CI:0.02,0.08) and SNAC-K (0.13SD 95%CI:0.06,0.20) but not in NSHD nor Rotterdam. Those with larger network sizes (≥6 people) scored higher on executive functioning and processing speed tests, whereas those with frequent social contacts performed better on executive functioning tasks only. Higher participation in social activities and greater perceived positive/less negative social support were associated with higher scores on all cognitive domains. Associations between social health and the rate of cognitive decline varied by social health marker, cognitive domain and study; generally, better social health was associated with a slowing of decline (<0.02 SD/year).Various measures of social health are related to cognitive capability in different ways. These findings may guide future studies to determine if promoting social health at old age may deter cognitive decline.