Self-management is widely accepted to improve patients’ health and reduce healthcare costs. Self-management focuses on active participation and taking responsibility in decisions in managing symptoms, treatment, physical and psychosocial consequences of living with a chronic condition. Patients struggle to self-manage their condition in their daily life. In primary care, nurses have a pivotal role in supporting patients in their self-management. Interventions to support patients to self-manage their condition are increasingly evaluated. Although self-management interventions have proven their effectiveness, it is not fully understood how these interventions work and which patients benefit. Furthermore, it is unclear to which extent self-management support is integrated in primary care. In this thesis, we aimed to unravel how self-management interventions work and which patients benefit from these interventions within a primary care setting. We aimed to examine how and to what extent nurses provide self-management support in their current practice. We found that nurses provided self-management support briefly and fragmented throughout their consultations. Nurses seldom focused on behaviour change. Subsequently, we developed and evaluated a behaviour change intervention (the Activate intervention) for patients at risk for cardiovascular disease delivered by nurses in primary care. The intervention was developed using the Behaviour Change Wheel and aimed to improve patients’ physical activity and equipped nurses with the competences to deliver the intervention. Patients were supported in four consecutive consultations over a three-month period by their primary care nurse. Nurses were trained to deliver the intervention. The Activate intervention was evaluated in a two-armed cluster-randomised controlled trial in 31 Dutch general practices and 195 patients during a follow-up period of 6 months. Patients reported that the intervention helped them to increase their physical activity but overall we did not find a significant increase in physical activity and other patient-related outcomes. We observed favourable effects in patients with a low acuity of perceived social support and in patients with a low baseline level of physical activity. Mixed methods evaluation among patients valued the self-monitoring tools and nurse-led support. Patients felt that having a trustful relationship with their nurse was crucial in order to increase their physical activity. Qualitative evaluation among nurses showed that nurses were positive about delivering the intervention and its effectiveness. Nurses felt the training facilitated them to acquire the competences needed to deliver the intervention. Implementation in routine care is challenging because of nurses’ tendency to relapse into their old consultation style and time constraints. The evaluation of fidelity of delivery showed that nurses delivered most of the intervention components as intended. Nurses’ beliefs about their capability, motivation, confidence and effectiveness towards the intervention delivery increased during the trial. However, several methodological factors and nurses’ variation in delivery of the intervention might have affected the quality of delivery and therefore might have diluted the effectiveness of the Activate intervention. To meet the promising expectations of self-management, nurses need to be adequately equipped with competences to provide self-management support and the healthcare system need to be adapted to facilitate self-management support.