Chronic Pain (CP) is a condition characterized by pain that lasts or recurs for more than three months in one or more parts of the body. This type of pain is often accompanied by emotional distress and difficulties in daily functioning, which can interfere with a person's ability to carry out everyday activities and maintain social roles. As a result, it places a considerable burden not only on individuals but also on national healthcare systems, due to both direct medical costs and indirect costs such as reduced work productivity and increased use of health services. Traditional treatments for CP, such as medications and surgical procedures, often fail to provide sufficient relief or significantly improve the quality of life of those affected. This has led to growing interest in alternative approaches that can offer more lasting and comprehensive support. In this context, psychological therapies have gained increasing attention, particularly Acceptance and Commitment Therapy, or ACT. This therapeutic approach focuses not only on the reduction of physical symptoms but also on helping people accept their pain as part of their lived experience. The goal is to promote emotional well-being and improve overall functioning by increasing what is known as psychological flexibility. ACT is particularly relevant for people suffering from CP, as it helps them lead a meaningful life despite the presence of pain. Instead of avoiding or fighting the pain, individuals are encouraged to accept it while committing to actions that align with their personal values. This process supports emotional regulation and encourages engagement in activities that bring a sense of purpose and satisfaction. However, access to this type of psychological intervention remains limited in many contexts. Barriers such as long waiting lists, lack of trained professionals, geographic distance from treatment centers, stigma associated with psychological therapy, and patients' physical limitations often make it difficult for those in need to receive adequate care. In response to these challenges, recent years have seen the development of new forms of digital health support. In particular, internet-delivered self-help programs have emerged as a promising solution for the treatment of CP. These programs can reach individuals who might otherwise be unable to access care and offer a flexible, low-cost, and convenient alternative to traditional face-to-face therapy. Research has shown that ACT can be effectively adapted and delivered online, allowing people to benefit from its therapeutic principles in a format that fits their needs and lifestyles. The current study aims to evaluate the effectiveness of a guided online self-help program based on Acceptance and Commitment Therapy for individuals with CP. The program is designed to help participants accept their pain and focus on improving their quality of life through value-based actions. The study will also explore the psychological mechanisms that may explain how and why the intervention works, with the goal of improving the design and delivery of future programs. Furthermore, the study will examine the cost-effectiveness of this type of digital intervention, in order to assess its potential for broader implementation within public health systems. By increasing access to evidence-based psychological care through digital platforms, this research seeks to contribute to more effective, inclusive, and sustainable treatment options for those living with chronic pain.