A significant and growing number of people work long hours. Research examining impacts is limited, but raises concerns about risks to the worker, the family, the employer, and the community. The purpose of this report, which is authored by the National Occupational Research Agenda (NORA) Long Work Hours Team, is to motivate and guide future research by proposing a framework for studying long work hours and discussing research gaps. The NORA Long Work Hours Team examined research reports and literature reviews, and gathered input from a conference on long work hours organized by the Team and faculty from University of Maryland. A framework is proposed for long work hours, including determinants, outcomes, and moderating factors of long work hours, suggesting that studies need to include more clear and complete descriptions of work schedules, worker characteristics, and the work environment, and need to consider a wider range of possible health, safety, social and economic outcomes for workers, families, employers, and the community. Additional studies are needed on vulnerable employee groups and those critical to public safety. More studies are also needed to develop interventions and test their effectiveness.