Membership of the cabinet is regulated by Article 28 of the Constitution of Ireland and by the Ministers and Secretaries Acts 1924 to 2017. The Irish constitution requires the government to consist of between seven and fifteen members, all of whom must be a member of the Oireachtas.
Since the formation of the 12th Government of Ireland in 1966, all Irish cabinets have been formed with the constitutional maximum of fifteen ministers. The total sometimes falls below this number for brief periods following the resignation of individual ministers or the withdrawal of a party from a coalition.
No more than two members of the cabinet may be members of Seanad Éireann. All other members of the cabinet must be members of Dáil Éireann, the house of representatives. The Taoiseach, Tánaiste and Minister for Finance must be members of the Dáil. In practice, however, the members of the cabinet are invariably members of the Dáil. Since the adoption of the 1937 constitution, only two ministers have been appointed from the Seanad: Seán Moylan who served in 1957 as Minister for Agriculture and James Dooge who served as Minister for Foreign Affairs from 1981 to 1982. (Joseph Connolly, a member of the Free State Seanad, had served in the Executive Council of the Irish Free State from 1932 to 1933 as Minister for Posts and Telegraphs, and from 1933 to 1936 as Minister for Lands and Fisheries.)
Members of the government in charge of Department of State are designated Ministers of Government (before 1977 a Minister of State). For distinction, Ministers of State (known before 1977 as Parliamentary Secretaries) — informally called junior ministers — are not members of the Government, but assist the Government Ministers in their Departments. A minister without portfolio may be appointed to the Government who is not the head of a Department of State; this occurred in 1939 during the period of the Emergency when Frank Aiken served as Minister for the Co-ordination of Defensive Measures until 1945.