Because nitrogen emissions from agricultural sources are geographically dispersed, cannot be easily observed, and are difficult to precisely control, this problem presents unique challenges for effective policy design. A suite of integrated practice and policy solutions may be needed to achieve both adequate source control and mitigation of the existing N stock within reasonable time frames. This chapter provides an overview of available policy instruments for nonpoint source pollution control and examines specific outcomes when these mechanisms have been implemented to control nitrogen pollution in practice. Policy characteristics are then organized into a coherent methodology for assessing candidate policies for controlling nitrogen emissions from agricultural sources in California.