The National Academies Keck Futures Initiative was launched in 2003 to stimulate new modes of scientific inquiry and break down the conceptual and institutional barriers to interdisciplinary research. At the Conference on Complex Systems, participants were divided into twelve interdisciplinary working groups. The groups spent nine hours over two days exploring diverse challenges at the interface of science, engineering, and medicine. The groups included researchers from science, engineering, and medicine, as well as representatives from private and public funding agencies, universities, businesses, journals, and the science media. The groups needed to address the challenge of communicating and working together from a diversity of expertise and perspectives as they attempted to solve complicated, interdisciplinary problems in a relatively short time. The summaries contained in this volume describe the problem and outline the approach taken, including what research needs to be done to understand the fundamental science behind the challenge, the proposed plan for engineering the application, the reasoning that went into it and the benefits to society of the problem solution.