Fortuna Huiusce Diei was an aspect of the goddess Fortuna, known primarily for her temple in the Area Sacra di Largo Argentina at Rome. Cicero lists her among the deities who should be cultivated in his ideal state, because "she empowers each day". She thus embodies an important aspect of time as it figures in Roman religion: every day of the year had a distinct and potent nature, which the public priests were responsible for knowing and aligning the community with by means of the religious calendar.

Fortuna is the goddess of fortune and the personification of luck in Roman religion who, largely thanks to the Late Antique author Boethius, remained popular through the Middle Ages until at least the Renaissance. The blindfolded depiction of her is still an important figure in many aspects of today's Italian culture, where the dichotomy fortuna / sfortuna plays a prominent role in everyday social life, also represented by the very common refrain "La [dea] fortuna è cieca".