The mission of the National Institute for Occupational Safety and Health (NIOSH) is to generate new knowledge in the field of occupational safety and health and to transfer that knowledge into practice for the betterment of workers. Since its establishment in 1970, NIOSH has provided national and world leadership in efforts to prevent occupational hearing loss. In 1996, NIOSH established the National Occupational Research Agenda (NORA). Because occupational hearing loss is one of the most common occupational illnesses among American workers, it was identified as one of the original 21 priority research areas, and a NORA Hearing Loss Team was established. The NORA Hearing Loss Team was composed of representatives from industry, academia, labor, professional organizations, and other governmental agencies. The team was tasked with developing a national research agenda for the prevention of occupational hearing loss. Each team member contributed to the original draft, which continued to evolve over time. The current document represents the culmination of several years of deliberation and revision. To best accomplish its goal of identifying needed research to prevent occupational hearing loss, the document is divided into two major sections: (1) defining the problem and (2) addressing the problem. The first major section, "Defining the Problem," includes 14 subsections. Preventing hearing loss and other adverse effects of occupational exposure to noise and ototoxic agents requires an understanding of the extent of the problem, the mechanisms that underlie these effects, the factors that contribute to their development or prevention, and their consequences. Although hearing loss has been recognized as an occupational hazard since the earliest days of industrialization, the magnitude of the problem in terms of number of workers exposed, prevalence of resulting impairment, and economic consequences has been estimated but not always well quantified. In addition, there is still much to learn about the impact of occupational noise and hearing loss on job performance, communication, and safety. A better understanding of these factors could help raise the sense of urgency that has been lacking for eliminating this preventable occupational injury. Furthermore, defining the mechanisms by which noise and chemicals lead to hearing loss and tinnitus is an important step in developing new preventive strategies. Identifying factors that affect or alter susceptibility to hearing damage may open additional avenues for reducing risk. And understanding other extra-auditory effects of noise exposure may provide additional impetus for reducing this hazard in the workplace. This section of the white paper outlines what we know, what we don't know, and what we need to know to better understand the scope of the occupational noise problem. Although research on these issues will not directly reduce occupational hearing loss and other adverse effects of noise exposure, it will provide the underpinnings necessary to better address the problem. Defining the problem must occur in concert with addressing it. The second major section, "Addressing the Problem," has 11 subsections that are focused on more applied elements of occupational hearing loss prevention programs. Although there are many unanswered questions regarding the nature and scope of occupational hearing loss, it is not necessary to resolve all of them before acting to reduce the problem. In fact, from a certain standpoint, addressing the problem is especially important because it can have an immediate impact on reducing the incidence of occupational hearing loss. In reality, of course, these two arms of research must be accomplished simultaneously, the former informing the latter and the latter providing feedback to the former. Traditionally, the occupational noise problem has been addressed through the establishment of effective hearing loss prevention programs. These programs typically involve seven components: noise measurement (to identify persons at risk), noise control (to remove the hazard insofar as possible), hearing protection (to prevent hearing loss when noise levels cannot be sufficiently reduced), audiometric monitoring (to ensure that protective measures are adequate), training and motivation (to encourage workers to engage in protective behaviors), record keeping (to permit evaluation of successes and failures), and program evaluation (to identify and correct program weaknesses). This section of the document focuses on each of these components in turn, describing what has worked, what might work even better, and what questions need to be answered to develop more effective approaches to hearing loss prevention. In addition, this section identifies unique populations with special hearing loss prevention needs and discusses research that would enable these groups to be better protected against occupational hearing loss. This section also addresses treatment and rehabilitation issues for the many workers who have already sustained a work-related hearing impairment. Finally, the need to take hearing loss prevention beyond the occupational arena and into the overall public health arena is discussed. In the past, NIOSH research has focused primarily on noise as the problematic exposure and hearing loss as the preventable outcome. However, exposure to ototoxic chemicals and outcomes such as tinnitus and various other adverse effects of noise have gained prominence in recent years. Although these additional exposures and effects are discussed in this document and related research has been recommended, most of the measures integral to programs for prevention of hearing loss-in particular, engineering noise control-could be expected to reduce the likelihood of these other adverse effects as well. In some cases, however, care must be taken that reducing one exposure does not increase another. Because each of the 25 subsections addresses a specific issue, such as mechanisms of noise-induced hearing loss, extra-auditory effects of noise exposure, noise control, and audiometric monitoring, each subsection can be thought of as a stand-alone discussion of the topic area. As such, each subsection has its own list of research needs. It should be noted that the NORA team elected not to list research needs in any specific order. This was in recognition of the fact that between work sectors, research needs would vary; the needs most highly prioritized in the mining sector, for instance, might be different than in the services or manufacturing sectors. Rather than providing a prioritized list of research topics, with the current document the team sought to provide a comprehensive assessment of the current state of hearing loss prevention technology and to provide broad direction for future research. However, NIOSH has adopted a strategic plan that does include prioritized research goals for preventing occupational hearing loss. More information about these prioritized research goals can be obtained on the NIOSH Web site, at <a href="https://www.cdc.gov/niosh/programs/hlp/goals.html"target="_blank">www.cdc.gov/niosh/programs/hlp/goals.html</a>.