Discussion of public and patient involvement (PPI) in health economics (HE) research is growing. There is much literature on PPI principles and standards, but little specifically regarding involving patients in HE research. Here, we outline "PACTS", a set of principles, developed with a PPI group, for considering patient involvement in HE research. Planning: Involvement is best built in to research plans from the outset. This includes setting specific goals for involvement activities, and clearly communicating the background and purpose of involvement. Approach selection: We describe two main approaches to involvement-discussion-based and task-based. Discussion-based approaches are useful for generating broad insights and revealing "unknown unknowns". Task-based approaches offer a more focused means of shedding light on "known unknowns". Continuous involvement: Involving patients throughout the research process and across a range of projects helps build expertise for patients and insight for HE researchers. Team building: Meaningful involvement creates a shared sense of ownership of the research and, over time, helps to develop a team ethos, enhancing the positive impacts of involvement. Sensitivity: HE research can be perceived as technical and impersonal. Addressing this requires sensitivity, clarity, and an honest and open approach. There is increased recognition that patient contributors are experts at providing a "lived experience" perspective, in the way that clinicians are experts at providing an overview of conditions and HEs are experts in the methodology of their discipline. We hope these "PACTS Principles" complement existing PPI approaches and provide a useful foundation for health economists considering patient involvement.