The present dosimetry file consists of 36 reactions in 26 isotopes and is being issued with Version IV of the ENDF/B library. The file evolved from the efforts of the Normalization and Standards Subcommittee of the Cross-Section Evaluation Working Group to review the status of multigroup cross-section sets used for dosimetry purposes in the Interlaboratory LMFBR Reaction Rate (ILRR) program. The recommendation of the subcommittee was the creation of a multigroup library based on the best available estimates of microscopic data even though these data might not initially agree with some of the integral tests. A task force to assemble this library was drawn from the subcommittee and member laboratories in the ILRR program. The library was tested with procedures similar to those used on the ENDF/B general file. Phase-I tests included processing with computer codes CHECKER to be sure the dosimetry file complied with the standard ENDF format and INTER to calculate the resonance integral of the exoergic reactions in the file. Phase II consisted of calculating spectrum-averaged cross sections with a variety of spectra and comparing the results with designated integral results.