The workplace is where 156 million working adults in the United States spend many waking hours, and it has a profound influence on health and well-being. Although some occupations and work-related activities are more hazardous than others and face higher rates of injuries, illness, disease, and fatalities, workers in all occupations face some form of work-related safety and health concerns. Understanding those risks to prevent injury, illness, or even fatal incidents is an important function of society. Occupational safety and health (OSH) surveillance provides the data and analyses needed to understand the relationships between work and injuries and illnesses in order to improve worker safety and health and prevent work-related injuries and illnesses. Information about the circumstances in which workers are injured or made ill on the job and how these patterns change over time is essential to develop effective prevention programs and target future research. The nation needs a robust OSH surveillance system to provide this critical information for informing policy development, guiding educational and regulatory activities, developing safer technologies, and enabling research and prevention strategies that serves and protects all workers. A Smarter National Surveillance System for Occupational Safety and Health in the 21st Century provides a comprehensive assessment of the state of OSH surveillance. This report is intended to be useful to federal and state agencies that have an interest in occupational safety and health, but may also be of interest broadly to employers, labor unions and other worker advocacy organizations, the workers' compensation insurance industry, as well as state epidemiologists, academic researchers, and the broader public health community. The recommendations address the strengths and weaknesses of the envisioned system relative to the status quo and both short- and long-term actions and strategies needed to bring about a progressive evolution of the current system.