This systematic review examines theoretical and empirical research on the psychological well-being of grandparents who provide supplementary care for their grandchildren. The review included 15 articles that met inclusion criteria. Seven of these studies examined the association of the provision of supplementary grandchild care to grandparents' psychological well-being, and the other eight studies analyzed the relations between specific characteristics of grandparents providing supplementary childcare and their own psychological well-being. The results suggested that the relationship between the provision of supplementary grandchild care and psychological well-being varies according to grandparents' socio-demographic characteristics (e.g. race and co-residence with adult children), caregiving situations (e.g. types of care and activities with grandchildren), and indicators of social capital (e.g. familial relationships and social supports). This paper highlights the limitations of the theoretical frameworks that have been used to explain the relationship between the provision of supplementary grandchild care and grandparents' psychological well-being in the studies that were reviewed, the strengths and limitations of related empirical research, and the lack of attention to diverse ethnic groups in reviewed studies. Suggestions for theory and future research are discussed based on these findings. (author abstract)