Katarche (καταρχή) is an ancient Greek word meaning a "beginning" or "inception."
One of the older applications of the term was within the context of religious rituals to refer to the moment when the sacrifice was first offered, or when the beginning or inception of the sacrifice took place.
The main application of the term "katarche" in the Hellenistic and Roman period was to the branch of astrology now called electional astrology, or the art of choosing an auspicious time to begin a venture or an enterprise.
Also included in this practice were techniques for analyzing an astrological chart drawn up for the beginning moment of an event that had already taken place, in order to foretell the likely success of a venture, or the timing of its development.
According to this modern interpretation there is a fluid connection between the notions of electional and horary astrology.