The Brookings Center on Social Dynamics and Policy applies complex systems science to the study of social dynamics and their implications for policy, mainly through the use of computational modeling and simulation. In a policy setting, complexity refers to situations in which responses to policy change may not be uniform or intuitive, due in part to feedback effects, time delays, interconnectedness, and non-linearity. In such situations, approaches from complex systems science can offer important advantages for the understanding of emergent social phenomena and the crafting of effective policy.