This formula index contains the compounds of all three volumes. The molecular formulae show metal atoms first, followed by carbon, hydrogen, and other nonmetal atoms arranged alphabetically. The monometallic and homo- polymetallic compounds are followed by hetero-bimetallic, -trimetallic, and -polymetallic compounds. Heterometallic compounds are listed under each metal. To make the use of the index easier, for the most part, simplified linear structural formulae are given after the molecular formulae. In the case of compounds containing complicated structures, such as fused carbocyclic, hetero- cyclic, or spiro rings, index names or a combination of group symbols and the parent compound names are used. Polymeric compounds are listed under their monomer formulae. Arseno, antimono, and bismutho compounds appear under their monomeric formulae. Arsenomethane and arsenobenzene, which were isolated as a pentamer and hexamer, respectively, and also as oligomers, are listed under their monomeric formulae and under Ass and Ase, respectively. The reference fiven at the end of each entry includes the volume number under- scored, followed by the page number. An asterisk following a reference page number signifies that the name or formula of this compound in the text was corrected. The lists of corrections and additions to the three volumes are appended to this volume. Several compounds missed in the main body of this index are compiled in the Additions section. We wish to express our appreciation to Mrs. Mary Alice Doiron for her perse- verance shown in the preparation of this typescript.