Nearly 69 percent of U.S. adults and 32 percent of children are either overweight or obese, creating an annual medical cost burden that may reach $147 billion. Researchers and policy makers are eager to identify improved measures of environmental and policy factors that contribute to obesity prevention. The IOM formed the Committee on Accelerating Progress in Obesity Prevention to review the IOM’s past obesity-related recommendations, identify a set of recommendations for future action, and recommend indicators of progress in implementing these actions. The committee held a workshop in March 2011 about how to improve measurement of progress in obesity prevention.