Data published by 53 manufacturers for 241 various hearing protectors sold in the United States were collected and presented for the evaluation of the types and styles of hearing protectors available. Included were 108 earmuffs, 30 hard hat mounted earmuffs, 86 earplugs, and 17 semi aural devices. The real ear attenuation at threshold (REAT) was the method used to determine the amount of noise attenuation provided by a hearing protector, and the techniques involved in measuring REAT were described. Ratings systems of protector performance according to different methods were discussed. The compendium was organized in tables and appendices: tables one, two, and three contained listings for earplugs, ear canal caps, and earmuffs, respectively. For each hearing protection device, the tables included the make and model, type, material, compatibility features, special features, the test laboratory used by the supplier and the noise reduction rating as calculated by NIOSH using data supplied by the manufacturer. Appendices containing calculations for ratings systems, listings of laboratories used by suppliers, comparisons of actual and experimental results, and supplier/noise reduction ratings for each device were provided.