The Cardinal Secretary of State—officially Secretary of State of His Holiness The Pope—presides over the Vatican Secretariat of State, which is the oldest and most important dicastery of the Roman Curia. The Cardinal Secretary is regarded as being in charge of the political and diplomatic activities of the Holy See and is thus referred to as being the Holy See's "Prime Minister". Since 1991, Cardinal Secretaries have been Presidents of the Interdicasterial Commission on Particular Churches and Interdicasterial Commission for the Church in Eastern Europe.