The catalog provides a single spectral type for each star listed in the La Plata catalog (Jaschek, Conde and de Sierra 1964; catalog <III/18>) and in the MK Extension (Kennedy 1978; see catalog <III/78>). In all cases the classifications are selected from those in the literature and have not been made by the author specifically for this compilation. A selected classification is considered to be the best one but is not necessarily a good one. If only one classification exists for a given object, it is given, regardless of its quality. The classifications were selected using a weighting system, with highest weight being given to classifications made by Morgan and/or Keenan, somewhat lower weight to those made by other spectral classification experts and various lower weights to those made by other workers. Classifications using designations that do not appear in the MK system have been excluded, as have objective-prism classifications, except where no slit spectra were available. The catalog contains a running number in one of the original catalogs (sequential numbers in the machine versions), identification of the original catalog, star identification (HD, DM, miscellaneous designations), equatorial coordinates (B1900), magnitude, V if available, m(v) otherwise) for reference purposes, reference number in the original catalog, selected classification, dispersion information, and standardized reference.