The engagement of patients and the public is increasingly important in the design and conduct of research. Some researchers still cling to the outdated notion that laypeople cannot contribute meaningfully to science; for some, "community engagement" is another term for recruiting patients for trials. Authentic engagement encompasses far more, involving stakeholders as full partners in all phases of research, as research funders increasingly require. Such engagement, although challenging, can enhance the quality and impact of studies on many levels, from ensuring that data are relevant to users' needs to elevating the moral plane of research by showing respect to patients and vulnerable populations. We share examples from our work, including the engagement of patients in a study of cancer screening decisions and the engagement of inner-city residents in addressing social determinants of health. These engagement principles are of growing relevance to health systems and policy makers responsible for population health.