Type 2 Diabetes (T2D) is a growing public health problem with potentially severe consequences for those affected. An unhealthy diet leading to being overweight combined with a sedentary lifestyle is considered a significant risk factor in the development of T2D. Changes in lifestyle, especially in diet and physical activity behaviors enabling sustained weight loss, can support T2D prevention. Changing lifestyle behaviors can, however, be challenging. Many individuals perceive intervention attendance and adherence as challenging. Behavioral interventions in T2D prevention are complex due to multiple interactions between intervention components and participants. This chapter discusses intervention complexity, mechanisms, and social-cognitive characteristics in T2D prevention interventions aiming for sustained weight loss. Social-cognitive factors refer to diverse attributes that may influence the success of behavior change. Here, self-efficacy, goal attainment, and participants’ sex and socioeconomic status are discussed. Challenges and potential solutions in designing and delivering T2D prevention interventions in primary care are reflected.