Purpose: We explored Bandura's self-efficacy theory as applied to older adult (aged 63-92) participation in physical and social activity in a cross-cultural study. Design and Methods: Older adults in Spain (n = 53) and the United States (n = 55) completed questions regarding self-efficacy, outcome expectancy, and participation in physical and social activities. Results: Self-efficacy significantly predicted both physical and social activity in both Spain and the United States. Outcome expectancy did not significantly predict either activity, nor did education, gender, or overall health. Modified and new self-efficacy measures proved reliable in both samples. Implications: This study enhances understanding of how self-efficacy motivates participation in physical activity, as noted in previous studies, as well as provides a new understanding of what motivates participation in social activities. The high reliability of the new measures used in this study provides evidence for further use of these measures in other contexts. It is important to note that this study further supports the use of Bandura's theory of self-efficacy for cross-cultural applications.