The USGCRP's Carbon Cycle Working Group asked the National Research Council's Committee on the Human Dimensions of Global Change 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-an understanding that can inform public decisions that could, among other things, prevent disasters from resulting from the ways humanity has been altering the carbon cycle. Members of the working group hoped that a successful workshop would improve communication between the relevant research communities in the natural and social sciences, leading eventually to an expansion of the carbon cycle program element in directions that would better integrate the two domains.