Workers' compensation (WC) provides medical care, cash benefits, and rehabilitation services to workers who experience occupational injury or illness. Because WC systems are intended to cover most occupational injuries and illnesses for most of the workforce, data produced in the operation of WC systems can be valuable for research, surveillance, and prevention activities that promote occupational safety and health (OSH). Such entities as academic and government researchers, public health authorities, and the insurance industry already use administrative data fRom, William N.C systems for research and surveillance. For a variety of reasons, however, the full potential of WC data to improve research and practice in OSH has not yet been realized. In recent years, the National Institute for Occupational Safety and Health (NIOSH) has undertaken a focused effort to advance the use of WC data, including the creation of the Center for Workers' Compensation Studies (CWCS). On December 11, 2014, NIOSH and the RAND Corporation hosted a colloquium designed to elicit input from key stakeholders in the OSH and WC communities on how CWCS could maximize the impact of its research activities. Participants offered examples of how CWCS and others currently use WC data. Several colloquium participants cited successful uses of WC data for surveillance and primary-prevention activities by state departments of public health. Early CWCS activities have focused on surveillance. Most CWCS work has involved working with key partners to develop and share methods. Although the primary focus of CWCS to date has been on insurance claim data, participants discussed many different sources of WC data in the course of the colloquium as well. As a source of occupational injury and illness data in the United States, WC data offer many unique advantages. Participants noted that few other data sources systematically identify injured workers. In contrast to WC data, data sets centered on the health care system seldom contain detailed information about patients' work environments or economic outcomes. Several participants also identified the ability to link WC data to outside data sources on the basis of worker, firm, or health care provider identifiers as a strength of WC data. In short, WC data are the best available resource for many surveillance activities and research questions. Participants also identified many limitations of WC data, however. They raised concerns about usefulness of WC data as a resource for surveillance and research and identified legal, contractual, and other barriers to the utilization of these data. One concern was that many injured workers do not file WC claims, so the universe of injuries that appear in WC data is a subset that is not necessarily representative of an industry or enterprise as a whole. Furthermore, changes in financial incentives, law, or administrative procedures for handling claims can also change the relationship between claim data and underlying injuries. Several participants also pointed out that the state-specific nature of WC systems makes it challenging to pool data from multiple state systems for some surveillance or research purposes. WC data often must be combined with other data sets to estimate quantities of interest, such as incidence rates, and some participants described incompatibilities between WC data and other data systems that can lead to difficulties. Because, in the vast majority of states, WC systems are privately financed and administered, participants identified fragmentation of data across payers and employers as a notable barrier to full utilization of WC data for research and surveillance. Participants also discussed other technical and institutional limitations of WC data. Participants discussed emerging trends within WC systems and the insurance industry and broader societal changes and innovations in analytic methods and data availability. They identified improvements in the quality of WC data, particularly the adoption of standardized electronic reporting systems, as an important trend that has increased the utility of WC data for analysts. Participants also discussed reforms to state WC systems and innovations in the WC insurance industry, noting that such changes can alter what WC data capture, so analysts must attend to them closely. Some participants suggested that CWCS might be interested in several new sources of occupational injury data that should be available in the future, and several participants voiced enthusiasm for expanded NIOSH support of linkages between WC data and administrative earning records, electronic medical records, or other external data sources. Participants also identified broader trends, such as population aging, health care reform, and changes in labor relations, as relevant to CWCS and the OSH research community. Participants formulated a variety of strategic and tactical considerations for CWCS in light of the issues discussed above. Participants articulated several features that make NIOSH unique, including its focus on workers, its mission to promote prevention of workplace injury and illness, and its nationwide scope. Although some participants argued that these considerations should urge NIOSH to focus narrowly on activities intended to prevent the occurrence of workplace injury and illness (or primary prevention), others argued that NIOSH could make a larger impact by focusing on disability prevention and occupational health services research as well. Participants identified a range of areas in which CWCS could make valuable contributions, including translation and dissemination of best practices in surveillance and prevention; facilitating partnerships between researchers and data providers; developing and evaluating interventions to improve workplace safety and return to work; research on institutional factors, including the design of WC systems and the organization of occupational health care; collaboration with the Occupational Safety and Health Administration; and investment in methodological research and the development of new worker-centered data sources. They also discussed suggestions for CWCS to promote these objectives in the short term.