Accountable care organizations (ACOs) are a promising payment model aimed at reducing costs while also improving the quality of care. However, there is a risk that vulnerable populations may not be fully incorporated into this new model. We define two distinct vulnerable populations, clinically at-risk and socially disadvantaged, and we discuss how ACOs may benefit each group. We provide a framework to use in considering challenges for both vulnerable patients and health systems on the path to accountable care. We identify policies that can help overcome these obstacles: strategies that support ACO formation in diverse settings and that monitor, measure, and reward the performance of providers that reach all patients, including vulnerable populations.