Knowledge of the natural and anthropogenic processes that affect the Earth’s energy balance is critical for understanding how climate has changed in the past and will change in the future. Effective metrics are needed to quantify and compare the various forcings that affect climate. For the past few decades, global mean radiative forcing at the top of the atmosphere has been reported extensively in climate change assessments, and it provides the foundation for policies directed at climate change. However, recent research on non-conventional climate forcing agents has raised doubts about the value and applicability of the radiative forcing concept. At the request of the U.S. Climate Change Science Program, the National Academies convened a committee to examine the current state of knowledge on radiative and non-radiative forcings of climate including contributions from greenhouse gases, aerosols, land-use changes, volcanoes, and solar variability. The committee was asked to identify key gaps in understanding, and to chart near- and longer-term research priorities for improving understanding and projections of climate forcings. The committee considered the radiative forcing concept itself, its continuing relevance in research and policy settings, and options for expanding the concept to account for non-conventional forcings such as aerosols and land-use changes. The findings and recommendations of this study will be presented.