Roman congregation

The second highest-ranking departments of the Roman Curia (the central administration of the Catholic Church) are called congregations. Above them are the three Secretariats. Lower-ranking are the pontifical councils and pontifical commissions. Others are tribunals and offices.

In origin, the congregations were selected groups of cardinals, not the whole College of Cardinals, commissioned to take care of some field of activity that concerned the Holy See. Today, as a result of a decision of the Second Vatican Council, the membership includes diocesan bishops from diverse parts of the world who are not cardinals. Each congregation also has a permanent staff to assist it in dealing with the business that comes before it.

Each congregation is led by a prefect, who is usually a cardinal. Until recently, a non-cardinal appointed to head a congregation was styled pro-prefect until made a cardinal. This practice has been abandoned.

Certain curial departments have been organized by the Holy See at various times to assist it in the transaction of those affairs which canonical discipline and the individual interests of the faithful bring to Rome. Of these the most important are, without doubt, the Roman Congregations (Sacræ Cardinalium Congregationes), as is evident from the mere consideration of the dignity of their membership, comprising cardinals who are officially the chief collaborators of the pope in the administration of the affairs of the Universal Church, though Cardinals have not always participated in the administration of ecclesiastical affairs in the same way.

Ecclesiastical business used to be handled by the pontifical chancery. However, the ever-growing number of business items and the ever-increasing complexity of the issues necessitated the creation of separate, specialised administrative-legislative bodies (the administrative and legislative functions of ecclesiastical government are not as sharply separated in the Catholic Church as in a secular government with the separation of powers).

...
Wikipedia