[1] According to the legend, the monastery was founded in 1136 by Siginand, prior of the abbey of Moutier-Grandval, who got lost in the deep forest of the High Jura while hunting a wild boar and was unable to find his way out.

[3] There are numerous spelling variations from the early years of the monastery: Balelaia, Belelagia, Belelai, Belilaia, Bellale, Bella Lagia, Bellelagia and Bellilagia.

[2] Bellelay was under the authority of the diocese of Basel, but operated as an independent lordship under the terms of a protection contract agreed with Bern and Solothurn (by 1414 at the latest) and also with Biel in 1516.

The abbey reached its golden age in the 18th century as a renowned place of education for the sons of European nobility.

The precious furnishings were sold at this time – an altar from Bellelay, for example, is now to be found in the parish church of Our Lady of the Assumption in Saignelégier.

The present structure of the abbey church of the Assumption was built by Franz Beer on the Vorarlberg Baroque model between 1708 and 1714.