In ancient Roman culture, felicitas (from the Latin adjective felix, "fruitful, blessed, happy, lucky") is a condition of divinely inspired productivity, blessedness, or happiness. Felicitas could encompass both a woman's fertility and a general's luck or good fortune. The divine personification of Felicitas was cultivated as a Roman goddess, wherein she is a goddess not just of good fortune but also happiness, wealth and success. Although felicitas may be translated as "good luck," and the goddess Felicitas shares some characteristics and attributes with Fortuna, the two were distinguished in Roman religion. Fortuna was unpredictable and her effects could be negative, as the existence of an altar to Mala Fortuna ("Bad Luck") acknowledges. Felicitas, however, always had a positive significance. She appears with several epithets that focus on aspects of her divine power.

Felicitas had a temple in Rome as early as the mid-2nd century BC, and during the Republican era was honored at two official festivals of Roman state religion, on July 1 in conjunction with Juno and October 9 as Fausta Felicitas. Felicitas continued to play an important role in Imperial cult, and was frequently portrayed on coins as a symbol of the wealth and prosperity of the Roman Empire. Her primary attributes are the caduceus and cornucopia. The English word "felicity" derives from felicitas.

In its religious sense, felix means "blessed, under the protection or favour of the gods; happy." That which is felix has achieved the pax divom, a state of harmony or peace with the divine world. The word derives from Indo-European *dhe(i)l, meaning "happy, fruitful, productive, full of nourishment." Related Latin words include femina, "woman" (a person who provides nourishment or suckles); felo, "to suckle" in regard to an infant; filius, "son" (a person suckled); and probably fello, fellare, "to perform fellatio", with an originally non-sexual meaning of "to suck". The continued magical association of sexual potency, increase, and general good fortune in productivity is indicated by the inscription Hic habitat Felicitas ("Felicitas dwells here") on an apotropaic relief of a phallus at a bakery in Pompeii.

In archaic Roman culture, felicitas was a quality expressing the close bonds between religion and agriculture. Felicitas was at issue when the suovetaurilia sacrifice conducted by Cato the Elder as censor in 184 BC was challenged as having been unproductive, perhaps for vitium, ritual error. In the following three years Rome had been plagued by a number of ill omens and prodigies (prodigia), such as severe storms, pestilence, and "showers of blood," which had required a series of expiations (supplicationes). The speech Cato gave to justify himself is known as the Oratio de lustri sui felicitate, "Speech on the Felicitas of his Lustrum", and survives only as a possible quotation by a later source. Cato says that a lustrum should be found to have produced felicitas "if the crops had filled up the storehouses if the vintage had been abundant if the olive oil had flowed deliberately from the groves", regardless of whatever else might have occurred. The efficacy of a ritual might be thus expressed as its felicitas.

The ability to promote felicitas became proof of one's excellence and divine favor. Felicitas was simultaneously a divine gift, a quality that resided within an individual, and a contagious capacity for generating productive conditions outside oneself: it was a form of "charismatic authority". Cicero lists felicitas as one of the four virtues of the exemplary general, along with knowledge of military science (scientia rei militaris), virtus (both "valor" and "virtue"), and auctoritas, "authority." Virtus was a regular complement to felicitas, which was not thought to attach to those who were unworthy. Cicero attributed felicitas particularly to Pompeius Magnus ("Pompey the Great"), and distinguished this felicitas even from the divine good luck enjoyed by successful generals such as Fabius Maximus, Marcellus, Scipio the Younger and Marius.

The sayings (sententiae) of Publilius Syrus are often attached to divine qualities, including Felicitas: "The people's Felicitas is powerful when she is merciful" (potens misericors publica est Felicitas).

Epithets of Felicitas include:

The cult of Felicitas is first recorded in the mid-2nd century BC, when a temple was dedicated to her by Lucius Licinius Lucullus, grandfather of the famous Lucullus, using booty from his military campaigns in Spain in 151–150 BC. Predecessor to a noted connoisseur of art, Lucullus obtained and dedicated several statues looted by Mummius from Greece, including works by Praxiteles: the Thespiades, a statue group of the Muses brought from Thespiae, and a Venus. This Temple of Felicitas was among several that had a secondary function as art museums, and was recommended by Cicero along with the Temple of Fortuna Huiusce Diei for those who enjoyed viewing art but lacked the means to amass private collections. The temple was located in the Velabrum in the Vicus Tuscus of the Campus Martius, along a route associated with triumphs: the axle of Julius Caesar's triumphal chariot in 46 BC is supposed to have broken in front of it. The temple was destroyed by a fire during the reign of Claudius, though the Muses were rescued. It was not rebuilt at this site.