The prevalence of diabetes continues to rise at an alarming rate, as do its financial costs and impact on quality of life. Preventing diabetes complications involves adhering to a labor-intensive self-care regimen, which requires considerable organization, self-regulation, and attention. This chapter provides an overview of the psychosocial and behavioral research in the area of diabetes, which includes the two vast and disparate literatures focused on type 1 diabetes (which largely focuses on children) and type 2 diabetes (which largely focuses on adults). In synthesizing the existing literature, we use self-determination theory as an organizational framework. Thus, our overview is not exhaustive in scope but instead reviews the relevant research that addresses individuals’ needs for competence, autonomy, and relatedness. Overall, the existing literature suggests that meeting these needs is likely to facilitate good health behaviors and maximize psychological well-being, both of which are connected to good physical health. Regardless of age, optimal interpersonal resources are those that involve support and facilitate autonomy while not undermining competence. Future research may benefit from the use of organizational theoretical frameworks—such as self-determination theory—in identifying mechanisms through which self-care, well-being and, ultimately, health may be improved.