This chapter presents and analyses six ethical rationales for patient involvement in HTA. We have identified three instrumental and three substantive rationales, namely, (1) relevance to healthcare goals and healthcare needs, (2) legitimacy leading to adherence to decisions, (3) capacity building via patient empowerment, (4) fairness and legitimacy through democratic participation, (5) fairness through respect for autonomy and (6) equity. Our ethical analysis finds that these rationales support patient involvement in HTA under specific premises. For example, relevance to healthcare goals and needs mainly support the use of patient-based evidence, while the other rationales require patient participation in some form. That is, for HTA to be legitimate enough to increase adherence, patients probably need to participate in the process and the same goes for equity. Likewise, when the rationales are democratic participation, empowerment and autonomy. Importantly, in order to achieve strong ethical support for patient involvement in HTA, it is crucial to ensure that these premises and their preconditions are fulfilled. On the other hand, all rationales raise issues of representation, i.e. which patient group should be represented through evidence or participation.