Festivals in ancient Rome were a very important part of Roman religious life during both the Republican and Imperial eras, and one of the primary features of the Roman calendar. Feriae ("holidays" in the sense of "holy days"; singular also feriae or dies ferialis) were either public (publicae) or private (privatae). State holidays were celebrated by the Roman people and received public funding. Games (ludi), such as the Ludi Apollinares, were not technically feriae, but the days on which they were celebrated were dies festi, holidays in the modern sense of days off work. Although feriae were paid for by the state, ludi were often funded by wealthy individuals. Feriae privatae were holidays celebrated in honor of private individuals or by families. This article deals only with public holidays, including rites celebrated by the state priests of Rome at temples, as well as celebrations by neighborhoods, families, and friends held simultaneously throughout Rome.

Feriae publicae were of three kinds:

One of the most important sources for Roman holidays is Ovid's Fasti, an incomplete poem that describes and provides origins for festivals from January to June at the time of Augustus.

Varro defined feriae as "days instituted for the sake of the gods." Religious rites were performed on the feriae, and public business was suspended. Even slaves were supposed to be given some form of rest. Cicero says specifically that people who were free should not engage in lawsuits and quarrels, and slaves should get a break from their labours. Agricultural writers recognized that some jobs on a farm might still need to be performed, and specified what these were. Some agricultural tasks not otherwise permitted could be carried out if an expiation were made in advance (piaculum), usually the sacrifice of a puppy. Within the city of Rome, the flamens and the priest known as the Rex sacrorum were not allowed even to see work done.

On a practical level, those who "inadvertently" worked could pay a fine or offer up a piaculum, usually a pig. Work considered vital either to the gods or preserving human life was excusable, according to some experts on religious law. Although Romans were required not to work, they were not required to take any religious action unless they were priests or had family rites (sacra gentilicia) to maintain.

Following is a month-by-month list of Roman festivals and games that had a fixed place on the calendar. For some, the date on which they were first established is recorded. A deity's festival often marks the anniversary (dies natalis, "birthday") of the founding of a temple, or a rededication after a major renovation. Festivals not named for deities are thought to be among the oldest on the calendar.

Some religious observances were monthly. The first day of the month was the Kalends (or Calends, from which the English word "calendar" derives). Each Kalends was sacred to Juno, and the Regina sacrorum ("Queen of the Rites," a public priestess) marked the day by presiding over a sacrifice to the goddess. Originally a pontiff and the Rex sacrorum reported the sighting of the new moon, and the pontiff announced whether the Nones occurred on the 5th or 7th of that month. On the Nones, announcements were made regarding events to take place that month; with the exception of the Poplifugia, no major festivals were held before the Nones, though other ceremonies, such as anniversaries of temple dedications, might be carried out. The Ides (usually the 13th, or in a few months the 15th) were sacred to Jupiter. On each Ides, a white lamb was led along the Via Sacra to the Capitolium for sacrifice to Jupiter.

The list also includes other notable public religious events such as sacrifices and processions that were observed annually but are neither feriae nor dies natales. Unless otherwise noted, the calendar is that of H.H. Scullard, Festivals and Ceremonies of the Roman Republic.