'St John's Co-Cathedral' is a guidebook about this gem of baroque art and architecture with its rich history and artistic heritage. This is due to the fact that for over 200 years it was the conventual church of the Order of St John of Jerusalem. The history of the Church is directly tied to the history of the Order in Malta over the years. The grandmasters, dignitaries and knights donated gifts of high artistic value and made enormous contributions to enrich it with the best works of art by the leading artists available to them. The knights themselves referred to the church as 'La nostra chiesa maggiore della Sacra Religione Gerosolmitana'.