St John's Co-Cathedral (Maltese: Kon-Katidral ta' San Ġwann) is a Catholic co-cathedral in Valletta, Malta, dedicated to Saint John the Baptist. It was built by the Order of St. John between 1573 and 1578, having been commissioned by Grand Master Jean de la Cassière as the Conventual Church of Saint John (Maltese: Knisja Konventwali ta' San Ġwann).