Festivals in ancient Rome were an 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 were of four kinds:

• Stativae were annual holidays that held a fixed or stable date on the calendar.
• Conceptivae were annual holidays that were moveable feasts (like Easter on the Christian calendar, or Thanksgiving in North America); the date was announced by the magistrates or priests who were responsible for them.
• Imperativae were holidays held "on demand" (from the verb impero, imperare, "to order, command") when special celebrations or expiations were called for.