Much has been written about the impact of involvement on research and the people involved, but much less is known about the impact on researchers. Based on previous experience of evaluating involvement, I was aware that researchers often report learning something new from involvement. Patients/the public bring 'new' knowledge to researchers, informed by their lived experience and use of services. I therefore carried out a narrative review of the literature to explore in depth what researchers learn from involvement. The findings confirmed that researchers often gain new knowledge and skills through involvement, which can change their priorities, values and attitudes. Therefore, researchers often directly experience the impact of involvement themselves. This learning then changes their practice. It leads them to change the design, delivery and dissemination of their research. Thus, many of the reported outcomes of involvement might be underpinned by what the researchers learnt through the process. Reframing impacts on research as impacts on researchers' learning has implications for practice and for motivating researchers to work with patients and the public. Further research and future evaluations of involvement might usefully explore the links between researchers' learning and outcomes.