Objective: The objective of this study was to examine the association between socioeconomic status (SES) and the onset of depression in older adults and to determine the relative contribution of psychosocial factors, physical health status, and behavioral factors in explaining this link. Methods: Data were from 2593 men and women, aged 55-85 years, participating in the Longitudinal Aging Study Amsterdam. Two indicators of SES were used: education and income. The onset of depression was measured over 9 years of follow-up. Results: Adjusted hazard ratios of incident depression were significantly higher in those with low education and low income. Psychosocial factors explained on average 16% of the SES differences in incident depression, physical health status on average 7%, and behavioral factors less than 5%. Conclusion: In older adults, low SES predicted the incidence of depression. Part of this association was explained by psychosocial factors and physical health status.