William Lilly was a seventeenth century English astrologer. He is described as having been a genius at something "that modern mainstream opinion has since decided cannot be done at all" having developed his stature as the most important astrologer in England through his social and political connections as well as going on to have an indelible impact on the future course of Western astrological tradition.

Western astrology is the system of astrology most popular in Western countries. Western astrology is historically based on Ptolemy's Tetrabiblos, which in turn was a continuation of Hellenistic and ultimately Babylonian traditions.