Assessments that are designed to be credible and useful in the eyes of potential users must rigorously evaluate the state of knowledge but also address the practical considerations— politics, economics, institutions, and procedures—that affect real-world decision processes. The Third US National Climate Assessment (NCA3) authors integrated a vast array of sources of scientific information to understand what natural, physical and social systems are most at risk from climate change. They were challenged to explore some of the potentially substantial sources of risk that occur at the intersections of social, economic, biological, and physical systems. In addition, they worked to build bridges to other ways of knowing and other sources of knowledge, including intuitive, traditional, cultural, and spiritual knowledge. For the NCA3, inclusion of a broad array of people with on-the-ground experience in various communities, sectors and regions helped in identifying issues of practical importance. The NCA3 was more than a climate assessment; it was also an experiment in testing theories of coproduction of knowledge. A deliberate focus on the assessment process as well as the products yielded important outcomes. For example, encouraging partnerships and engagement with existing networks increased learning and made the idea of a sustained assessment more realistic. The commitment to building an assessment focused on mutual learning, transparency, and engagement contributed to the credibility and legitimacy of the product, and the saliency of its contents.