Patient organisation involvement in health technology assessment (HTA) has evolved in line with an increased understanding among patient organisations, HTA bodies and health technology developers of the need to be informed by patient knowledge. Despite patient organisations’ varied remits, size, funding and reach capacity, they increasingly play a critical role in fostering effective patient involvement in HTA. Patient organisations often have a broad overview of the standard of care by disease area across different geographies, positioning them effectively to guide evidence generation about patients’ experiences, preferences and needs, participate in research and development across the health technology life cycle, including horizon scanning, to identify high priority interventions for evaluation, appraisal of individual health technologies and participation in HTA policy and process development. The ability to contribute on these matters requires disease-specific scientific knowledge, understanding of HTA policy and processes, data literacy skills, financial and human resources as well as regular training opportunities. This chapter describes how the advocacy role of patient organisations in HTA varies across regions and outlines important capacity development initiatives. To conclude, we reflect on ongoing challenges and explore opportunities for collaboration among patient organisations.