For a long time, patients were seen as weak and passive recipients of care, whose only role was to provide information and comply with doctors' orders. This is beginning to change, and patients are more seen as autonomous, active, and involved collaborators in care, co-creating value with service providers and others. In parallel, the healthcare sector is changing due to an aging population, advances in technology, medical knowhow, and the prevalence of chronic diseases, which all call for a more involved patient. During the last decade, patient involvement in healthcare has been recognized as important to provide more efficient, integrated, patient-focused healthcare. Despite this recent gain in attention, there is a gap between rhetoric's and practice, since the meaning and benefits of patient involvement are unclear both in theory and practice. This thesis takes an alternate perspective on patient involvement, departing from service theory on value creation and customer involvement. It aims to understand and explore patient involvement and how patients can be involved in both the use, and development, of healthcare services.This thesis is based on three different studies using both qualitative and quantitative research methods. The first study is a systematic literature review of healthcare research, addressing the topic of patient involvement and related concepts. Based on a total of 125 reviewed empirical articles, this study serves as an introduction and orientation to the diverse field. It aims to contribute to the knowledge base in the growing research field of patient involvement. The second study addresses and explores lead-user theory as a method to identify highly innovative patients who can be suitable for involvement in healthcare development. The third study explores how patients, depending on disease, care process and context, can take different roles in healthcare development.The results indicate that patient involvement is not an isolated activity but influences the whole healthcare system. This extends the view of patient involvement from just decision-making and isolated encounters to patients potentially being substantially involved in all aspects of healthcare. This is also important in involvement in use. The patient's individual experiences, context, and type of illness play an important role in development initiatives. Patients should be selected carefully, for involvement in healthcare development, depending on the goal of the initiative. The type of illness and the patient's context are key factors to the kind of contributions patients can make. Depending on the type of illness, and if it shows up mostly at home or at the care provider's, patients develop different contributions.This thesis contributes to understanding patient involvement by taking a service perspective on co-creation and customer involvement. This approach to patient involvement extends the traditional view by proposing that patients should be involved in all stages of healthcare. Understanding how individuals...