Context: For three decades, experts have been stressing the importance of law to the effective operation of public health systems. Most recently, in a 2011 report, the Institute of Medicine recommended a review of state and local public health laws to ensure appropriate authority for public health agencies; adequate access to legal counsel for public health agencies; evaluations of the health effects and costs associated with legislation, regulations, and policies; and enhancement of research methods to assess the strength of evidence regarding the health effects of public policies. These recommendations, and the continued interest in law as a determinant of health system performance, speak to the need for integrating the emerging fields of Public Health Law Research (PHLR) and Public Health Systems and Services Research (PHSSR). Methods: Expert commentary. Findings: This article sets out a unified framework for the two fields and a shared research agenda built around three broad inquiries: (1) the structural role of law in shaping the organization, powers, prerogatives, duties, and limitations of public health agencies and thereby their functioning and ultimately their impact on public health ("infrastructure"); (2) the mechanisms through which public health system characteristics influence the implementation of interventional public health laws ("implementation") ; and (3) the individual and system characteristics that influence the ability of public health systems and their community partners to develop and secure enactment of legal initiatives to advance public health ("innovation") . Research to date has laid a foundation of evidence, but progress requires better and more accessible data, a new generation of researchers comfortable in both law and health research, and more rigorous methods. Conclusions: The routine integration of law as a salient factor in broader PHSSR studies of public health system functioning and health outcomes will enhance the usefulness of research in supporting practice and the long-term improvement of system performance. © 2012 Milbank Memorial Fund.