In public health, law is the ultimate lightning. It is the law that does the work. Protection of health and safety is widely recognized as a core government function, and a recurring theme is the application of law to protect the public’s health. We have used the law to achieve public health goals in areas ranging from mandatory vaccinations, seat belt requirements, fl uoridation of water, reductions in drunk driving, improved workplace safety, and more. Although many public health outcomes can be reached through voluntary actions, the force of law is available as a tool when necessary. Disease surveillance, the foundation of public health practice, would be impossible if the law did not mandate reporting. We can address concerns about patient privacy and preserve confi dentiality with controls on how health data are collected and used. As the public health pioneer Hermann Biggs noted more than a century ago regarding tuberculosis reporting: “Notifi cation to sanitary authorities does not involve notifi cation to the city at large.”1 Despite the availability of eff ective medications for many diseases, some patients refuse treatment. In the case of communicable diseases such as tuberculosis, the law can compel people to remain isolated or accept treatment to ensure that they cannot infect others. The adage “Your right to swing your fi st ends where my nose begins” implies government’s duty to prevent individuals from acting in ways that imperil the health and safety of others.