This commentary describes the emergence of legal epidemiology, its key methods and tools, and the challenges it faces going forward. 

"Legal epidemiology" is the scientific study and deployment of law as a factor in the cause, distribution, and prevention of disease and injury in a population. Its emergence as a distinct field reflects the indispensability of law to modern public health practice. Proponents of the field aim to remove two persistent barriers to the effective use of legal action for public health: the limited extent of rigorous and timely evaluation of the impact of law and legal practices on health; and the inattention in training and practice to the important legal functions played by nonlawyers in the health system. 

In the authors' assessment, the research necessary to identify and spread best legal practices is too often never carried out. Legal interventions affecting millions of Americans are often not evaluated for years, if at all. Innovations that show promise in research or practice are sometimes not scaled, so they either do not spread or spread too slowly. The unintended (or incidental) effects of laws on population health often remain unidentified and unexplored. Limited professional training in law, disciplinary boundaries, and, arguably, a cultural tension between law and other health disciplines continue to limit the full integration of law into public health.

This article was originally published in a special supplement of the Journal of Public Health Management and Practice, "Advancing Legal Epidemiology," that presents 13 original articles using theory and methods from the field of legal epidemiology. The supplement issue includes nine original research articles and four commentaries that explore the past, present, and future of the field.