The caduceus is a herald's staff, a symbolic object representing Hermes (or the Roman Mercury), and by extension trades, occupations or undertakings associated with the god. It is today typically depicted as a short staff entwined by two serpents in the form of a double helix, and is sometimes surmounted by wings. This staff was was also borne by Iris, the messenger of Hera.

In later Antiquity the caduceus provided the basis for the astrological symbol representing the planet Mercury and in Roman iconography was often depicted being carried in the left hand of Mercury, the messenger of the gods, guide of the dead and protector of merchants, shepherds, gamblers, liars and thieves.

Hermes was an "Oriental deity of Babylonian extraction" represented in his earliest form as a snake god. From this perspective, the caduceus was originally representative of Hermes himself, in his early form as the Underworld god Ningishzida, "messenger" of the "Earth Mother".

It is relatively common, especially in the United States, to find the caduceus, with its two snakes and wings, used as a symbol of medicine instead of the correct rod of Asclepius, with only a single snake. This usage is erroneous, popularised largely as a result of the adoption of the caduceus as its insignia by the US Army medical corps in 1902 at the insistence of a single officer (though there are conflicting claims as to whether this was Capt. Frederick P. Reynolds or Col. John R. van Hoff