The caduceus (☤; /kəˈdjuːʃəs, -siəs/; Latin: cādūceus, from Greek: κηρύκειον kērū́keion "herald's wand, or staff") is the staff carried by Hermes in Greek mythology and consequently by Hermes Trismegistus in Greco-Egyptian mythology. The same staff was also borne by heralds in general, for example by Iris, the messenger of Hera. It is a short staff entwined by two serpents, sometimes surmounted by wings. In Roman iconography, it was often depicted being carried in the left hand of Mercury, the messenger of the gods.

Some accounts suggest that the oldest known imagery of the caduceus has its roots in a Mesopotamian origin with the Sumerian god Ningishzida; whose symbol, a staff with two snakes intertwined around it, dates back to 4000 BC to 3000 BC.

As a symbolic object, it represents Hermes (or the Roman Mercury), and by extension trades, occupations, or undertakings associated with the god. In later Antiquity, the caduceus provided the basis for the astrological symbol representing the planet Mercury. Thus, through its use in astrology, alchemy, and astronomy it has come to denote the planet and elemental metal of the same name. It is said the wand would wake the sleeping and send the awake to sleep. If applied to the dying, their death was gentle; if applied to the dead, they returned to life.

By extension of its association with Mercury and Hermes, the caduceus is also a recognized symbol of commerce and negotiation, two realms in which balanced exchange and reciprocity are recognized as ideals. This association is ancient, and consistent from the Classical period to modern times. The caduceus is also used as a symbol representing printing, again by extension of the attributes of Mercury (in this case associated with writing and eloquence).

The caduceus is often incorrectly used as a symbol of healthcare organizations and medical practice, particularly in the United States of America, due to confusion with the traditional medical symbol, the Rod of Asclepius, which has only one snake and is never depicted with wings (the logo of the World Health Organization uses the Rod of Asclepius as its basis).