Summary: The U.S. Global Change Research Program (USGCRP) has identified the global carbon cycle as a major program element. An interagency Carbon Cycle Working Group guided by a Carbon Cycle Science Plan (CCSP) sets research directions for this effort. The CCSP and the scientific steering committee strongly reflect the intellectual concerns of fields of natural science that study the cycling of carbon through the atmosphere and the biosphere. Although the CCSP notes the critical role of human activities in perturbing the carbon cycle, it does not include any research on these activities. The U.S. government’s carbon cycle research activity has not yet integrated the relevant fields of the social and behavioral sciences. It is in this context that the USGCRP’s Carbon Cycle Working Group asked the National Research Council to hold a workshop on Human Interactions with the Carbon Cycle. The basic purpose of the workshop was to help build bridges between the research communities in the social sciences and the natural sciences that might eventually work together to produce the needed understanding of the carbon cycle.