The Abbey of Monte Oliveto Maggiore is a large Benedictine monastery in the Italian region of Tuscany, 10 km south of Asciano.

It is the mother-house of the Olivetans and the monastery later took the name of Monte Oliveto Maggiore ("the greater") to distinguish it from successive foundations at Florence, San Gimignano, Naples and elsewhere.

On 18 January 1765, the monastery church was made the seat of the Abbey nullius of Monte Oliveto Maggiore, meaning it had exemption from the local diocese as a quasi-diocese in its own right.

The monastery is accessed through a drawbridge which leads to a medieval palace in red brickwork, surmounted by a massive quadrangular tower with barbicans and merlons.

Over the entrance arch is a terracotta depicting Madonna with Child and Two Angels attributed to the Della Robbia family, as well as the St Benedict Blessing nearby.

The frescoes of the Life of St. Benedict painted by Luca Signorelli and il Sodoma, located in the cloister lunettes under the vaults, are considered masterworks of the Italian Renaissance.

From the library is the access to the Pharmacy, housing a collection of medicinal herbs in 17th-century vases, The name Definitorio refers to the Capitular Hall (1498), on whose end wall is a fresco of Madonna with Child and Saints by Matteo Ripanda (16th century); the hall houses a small museum of Sacred Arts, with works by Segna di Bonaventura (Madonna with Child), the Master of Monte Oliveto (Maestà), Neroccio di Bartolomeo (St. Bernardino), Vincenzo Tamagni (Madonna with Child) and a fresco portraying St. Sebastian by an artist of the Sienese School.