This discussion builds on the significant advances in patient and public involvement (PPI) in health technology assessment (HTA) over the past two decades. It draws on key concepts that are raised in the early chapters in this Part with a view to refining our understanding of these concepts so that the development of thinking in this arena can continue to evolve. The discussion is framed around four key concepts: decision-making, the functional difference between patient and public involvement, representation, and epistemic injustice. Firstly, the discussion distinguishes between the HTA process and the final decision-making step, advocating for patient involvement in evidence gathering but public involvement in decision-making to ensure fairness. Secondly, it examines the concept of representation, differentiating between descriptive and political representation, and emphasises the importance of clear roles for PPI contributors. Thirdly, the issue of epistemic injustice is addressed, focusing on testimonial and hermeneutic injustices that patients may face. By examining the contrary, epistemic justice, the discussion argues for the proper treatment of patient knowledge and the provision of appropriate forums for expression. Overall, the discussion suggests that refining these distinctions will enhance the rationale and practice of PPI in HTA, leading to more nuanced practice and just healthcare provision.