The Knights Hospitaller was a religious order of monks who based themselves in Jerusalem in order to take care of pilgrims who had made the arduous journey from Europe to the Holy Land.

For many Christians a pilgrimage to the Holy Land was an important part of their lives. Even before the fall of Jerusalem they travelled from all over Europe to reach the Holy City. Many pilgrims were attacked and killed as they made their way across the Middle East, but those who reached Jerusalem were often starving, weak and poor. A group of monks led by Gerard, a knight from Provence, set up a hospital to attend to the needy pilgrims. This hospital was named after St. John the Compassionate, a Patriarch of Alexandria. The monks who worked in the hospital lived under a strict rule and accepted no luxuries. The order of monks became known as the Knights Hospitaller. The Hospitallers were able to run their affairs from donations given to them by travellers or other who just wanted to support their work. After Jerusalem was captured the new rulers recognised the good work that the monks did and granted them land so that they could have a steady income.

A Papal Bull (a formal proclamation issued by the pope) recognised and named the Knights Hospitallers of St. John of Jerusalem as an independent religious order in 1113.

The Hospitaller order inspired the foundation of another group of knights called the Knights Templar, based in and around Jerusalem, whose purpose was to protect the pilgrims as they travelled towards the Holy City.