The Diocese of Alajuela () is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Costa Rica. It is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of San José de Costa Rica. The Diocese of Alajuela was erected on 16 February 1921.
Bishops
Ordinaries
Antonio del Carmen Monestel Zamora (1921–1937) Víctor Manuel Sanabria Martínez (1938–1940), appointed Archbishop of San José de Costa Rica Juan Vicente Solís Fernández (1940–1967) Enrique Bolaños Quesada (1970–1980) José Rafael Barquero Arce (1980–2007) Angel San Casimiro Fernandez, O.A.R. (2007–2018) Bartolomé Buigues Oller, T.C. (2018- )