It is formed by the Mayor (Alcalde) and the elected councillors, who compose the Plenary (Pleno). In municipalities with over 5000 inhabitants, a Government Commission (Junta de Gobierno or Comisión de Gobierno) is mandatory, while the existence of the body in municipalities under that population is at the discretion of the Plenary or the organic regulations of the Ayuntamiento.
After the 1978 Spanish Constitution, the Ayuntamiento follows a collegiate-representative model, with features of a corporative organism such as the double presidency of both the deliberative body (the Plenary) and the executive body by the Mayor, and the formation of the Government Commission exclusively by elected councillors. The indirect election of the Mayor by the councillors, stated in the 1978 Law of Local Elections was confirmed in the 1985 Organic Law of the General Electoral Regime. The system of municipal organization is described in the 1985 Law Regulatory of the Basis of the Local Regime (LRBRL). A 11/1999 Law superseding some features of the LRBRL set increased powers for the Mayor, gaining in turn the Plenary more scrutiny powers over him. The Plenary lacks legislative autonomy.
The municipalities of Madrid and Barcelona have a special regime, regulated by the 2006 Law of Capitality and Special Regime in the case of the Ayuntamiento of Madrid and by the Municipal Charter of Barcelona, approved in the 22/1998 Catalan law in the case of Barcelona.