The astrological work of Ptolemy, usually called Tetrabiblos, or the Four Books, has in some manuscripts the title that Ptolemy himself apparently used, “Mathematical Treatise in Four Books.” This work is a systematic treatise on astrology. Although the Tetrabiblos enjoyed almost biblical authority among astrologers for more than a millennium, its Greek text was printed only three times. Numerous translations of Tetrabiblos have been published into different languages, from the most ancient, Arabic, in 1138, to medieval and modern translations into Latin, English, and German.