The 3rd supplement continues the updating of the original 20 volumes on boron compounds published between 1974 and 1979. The first supplement consisting of 3 volumes covered all the literature uniformly up to the end of 1977, whereas the two volumes of the 2nd supplement have extended the literature coverage of boron compounds to 1980 and the four volumes of the 3rd supplement to 1984. The present volume continues the description of boron compounds with halogens, presenting those with chlorine, bromine and iodine. The compounds with chalcogens are completed here along with those of boron with S, Se, Te and Po. The final chapter on carboranes contains the carboranes themselves, together with metallacarboranes, and in the last section a description of carborane-containing polymers, mostly derived from the three isomeric dicarbadodecarboranes. Volume 4 of the 3rd supplement brings this supplement series to an end. It will be supplemented by a separately appearing index volume, which contains all the boron compounds dealt with in volumes 1 - 4 of this supplement series.