This book contains a translation of the Introduction to the Tetrabiblos written by famous third century philosopher Porphyry. It is a sort of Astrological Dictionary, defining most of the technical terms used by the Greek astrologers of the Classical Period. The volume also contains a translation of the short treatise on astrological technical terms by Serapio of Alexandria. About the translator: James Herschel Holden, M.A. is the Research Director of the American Federation of Astrologers and has been especially interested in Classical and Medieval astrological works.