Tyche (; Ancient Greek: Τύχη Túkhē, 'Luck', Ancient Greek: [tý.kʰɛː], Modern Greek: [ˈti.çi]; Roman equivalent: Fortuna) was the presiding tutelary deity who governed the fortune and prosperity of a city, its destiny. In Classical Greek mythology, she is usually the daughter of the Titans Tethys and Oceanus, or sometimes Zeus, and at this time served to bring positive messages to people, relating to external events outside their control.

During the Hellenistic period, with dramatic socio-political changes starting with Alexander the Great, Tyche increasingly embodied the whims of fate (both negative and positive), eclipsing the role of the Olympic gods. The Greek historian Polybius believed that when no cause can be discovered to events such as floods, droughts, frosts, or even in politics, then the cause of these events may be fairly attributed to Tyche. Other ancient Greek sources corroborate Polybius, such as Pindar who claims Tyche could hand victory to a lesser athlete. This "Hellenistic Tyche" is often featured on coins such as those minted by Demetrius I Soter. Further, Tyche comes to represent not only personal fate, but the fate of communities. Cities venerated their own Tychai, specific iconic versions of the original Tyche. This practice was continued in the iconography of Roman art, even into the Christian period, often as sets of the greatest cities of the empire.

Tyche was further absorbed into the Parthian Empire, who frequently depicted Tyche in their coins, as well as in imagery bestowing legitimacy to Parthian kings.