Astrology is a group of systems, traditions, and beliefs in which knowledge of the relative positions of celestial bodies and related details is held to be useful in understanding, interpreting, and organizing information about personality, human affairs, and other terrestrial matters. A practitioner of astrology is called an astrologer, or, less often, an astrologist. Historically, the term mathematicus was used to denote a person proficient in astrology, astronomy, and mathematics.

Although the two fields share a common origin, modern astronomy is entirely distinct from astrology. Astronomy is the scientific study of astronomical objects and phenomena, whereas astrology is concerned with the attempt to correlate these phenomena with earthly affairs. Astrology is variously considered by its proponents to be a symbolic language, a form of art, science, or divination. The scientific community generally considers astrology to be a pseudoscience or superstition as astrologers have failed empirical tests in controlled studies.  Despite the lack of scientific evidence, belief in astrology is widespread.

The word astrology is derived from the Greek αστρολογία, from άστηρ (aster, "star") and λόγος (logos, "speech, statement, reason"). The -λογία suffix is written in English as -logy, "study" or "discipline".