St Osyth's Abbey (originally and still commonly known as St Osyth's Priory) was a house of Augustinian canons in the parish of St Osyth (then named Chich) in Essex, England in use from the 12th to 16th centuries. Founded by Richard de Belmeis, Bishop of London, c. 1121, it became one of the largest monasteries in Essex. It was dedicated to Saints Peter and Paul as well as St Osyth (Osith), a royal saint and virgin martyr. Bishop Richard obtained the arm bone of St Osyth from Aylesbury for the monastic church and granted the canons the parish church of St Osyth.