The College of Cardinals is the body of all Cardinals of the Roman Catholic Church. The College plays two roles in the church:

• participating in papal elections when the Holy See is vacant, and
• advising the Pope about Church matters when he summons them to an ordinary consistory.

Historically, they were also the clergy of the city of Rome serving the Pope as the Bishop of Rome and were assigned duties in parishes of the city. The College has no ruling power except during the sede vacante period, where its powers are still extremely limited according to the Apostolic constitution Universi Dominici Gregis.

The council has its origins in the events surrounding the crowning of Henry IV as King of Germany and Holy Roman Emperor at the age of six, after the unexpected death of Henry III in 1056. Up until this point secular authorities had significant influence over who was to be appointed Pope, and the Holy Roman Emperor in particular had the special ability to appoint him. This was significant as the aims and views of the Holy Roman Emperor and the Roman Catholic Church did not always coincide. Members of what was to become known as the Gregorian Reform took advantage of the new King and his lack of power, and in 1059 declared that the election of the Pope was an affair only for the Church. This was part of a larger power struggle, named the Investiture Controversy, as the Church attempted to gain more control over their clergy, and in doing so gain more influence in the lands and governments they were appointed to. Theological implications aside, its creation represented a significant shift in the balance of power in the Early Medieval world.

The Dean of the College of Cardinals and the Sub-Dean are the president and vice-president of the college. Both are elected by the cardinals holding suburbicarian dioceses, but the election requires Papal confirmation. Except for presiding, the Dean has no power of governance over the cardinals, instead acting as primus inter pares.

The Secretary of State, the prefects of the Congregations of the Roman Curia, the Camerlengo of the Holy Roman Church, the Vicar General of Rome, and the Patriarchs of Venice and Lisbon, are usually Cardinals, with few, generally temporary, exceptions.