Erlach Abbey (Abbaye Saint-Jean de Cerlier) also known as St. Johannsen Abbey (Kloster Erlach, otherwise Abtei St. Johannsen), was a Benedictine monastery in Gals, Canton of Bern, Switzerland.
It was founded between 1093 and 1103 by Kuno, Count of Fenis and Bishop of Lausanne, on an island in the Thielle. the foundation was completed after his death by his brother, Burchard, bishop of Basle. The new monastery was settled by monks from St. Blaise's Abbey in the Black Forest. The Vogtei, initially the property of the Counts of Fenis, passed from them to the Counts of Neuchâtel-Nidau, and from them at the end of the 14th century to the city of Berne, which in 1474-76 also acquired the lordship of Erlach.
The abbey was secularised in 1528-29. The nave of the abbey church was demolished, but the choir and transept remained, and was used as a grain store. These structures were also demolished in 1961 after they had become unsafe, but the quire was rebuilt in 1970-71. The conventual buildings remained standing, and in the 19th century were put to various industrial uses, until in 1883 the local government authority of Bern bought the site back and turned it into a prison. It continues in use as a detention centre for male adults.