There has been an ongoing controversy relative to hearing protector effectiveness. The American National Standards Institute (ANSI) sets consensus guidelines to measure hearing protector attenuation (S3.19-1974 through S12.6-1990). Beginning with Padilla in 1976, field studies have consistently shown that laboratory data greatly overestimate the attenuation typically received in the workplace. The ubiquitous NRR (noise reduction rating) also overpredicts actual workplace attenuation because it is derived from laboratory data. Occupational fit is usually poorer than laboratory fit. Reusable hearing protectors deteriorate due to repetitive use and aging of materials. Interaction with other protective equipment can reduce hearing protector attenuation. Both the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have proposed workplace attenuation derating factors for the NRR. However, the development of employer hearing protector fit testing procedures analogous to respirator fit testing in concert with a fully effective hearing conservation program will be the only effective answer to this question.