This article examines the vertical diffusion of a policy between a state and its local governments. Although policy diffusion typically relies upon multiple mechanisms, diffusion between a state and its local governments relies primarily on coercion. Using a case study of state-mandated adherence to Generally Accepted Accounting Principles (GAAP), we show that the coercion mechanism is dependent upon the capacity of the state and local governments to adopt and implement a policy, as well as the discretion available to a local government. Utilizing data from all 50 states as of 2008, our findings show that the vertical diffusion of a policy is reliant on a state’s fiscal capacity and the personnel capacity of the local government. We also found that strong institutional autonomy at the local level leads a state to adopt a GAAP mandate.