In October 2005 a group of approximately 120 experts on solar and space physics and the effects of radiation on humans and spacecraft met for a workshop at the Wintergreen conference facilities near Charlottesville, Virginia. This workshop followed other efforts by solar and space physics scientists to address ways in which their work could be focused on support for NASA’s Vision for Space Exploration (see Box P.1). These earlier meetings included a RHESSI-SOHO-TRACE Workshop in December 2004 that had recommended a meeting near Washington, D.C., in the fall of 2005 to bring together NASA Exploration operations and engineering personnel and scientists. It also followed a workshop organized by NASA’s Living With a Star (LWS) program, held on April 5-6, 2004, in Washington, D.C., to examine existing and planned LWS science missions that contribute to the enabling of proposed human lunar and Mars missions. At nearly the same time, the Committee on Solar and Space Physics (CSSP) of the National Research Council’s (NRC’s) Space Studies Board independently began planning for a study on space environmental hazards. The CSSP agreed to cosponsor the workshop and to prepare this NRC workshop report.