Patient participation refers to a range of activities which enable patients to contribute their knowledge regarding their needs, preferences, experiences and perspectives before, during or after individual HTAs, and to influence methods, processes, governance and policy. It complements research into these aspects. This chapter sets out the rationale for patient participation in HTA, the nature of patient knowledge and describes common practices, stressing the need for defined goals. It takes stock of reported challenges, enablers and barriers, before updating Facey’s (Patient involvement in health technology assessment. Springer Nature; 2017) mosaic of approaches to patient participation in line with evolving practice and conceptualisations to reveal a wealth of opportunities for participation in HTA. With the mosaic there is also the opportunity for HTA bodies and patient communities to consider which goals are most important and which approaches will best achieve them. It concludes with a reflection on the ongoing issues of inclusivity, power imbalance, burden and transparency of impact, and the use of participation to fill evidence gaps before raising questions about the suitability of the current focus of participation activities in HTA.