He wrote the lives of five of its abbots: Lanfranc, Archbishop of Canterbury, Gulielmus de Bellomonte, Boso, Theobaldus, and Letardus.
The other four (those of Theobaldus and Letardus being mere summaries) are included in the Patrologia Latina (Vol.
Milo must have been an old man when he wrote them, for in the last chapter of his life of Lanfranc he relates something which he himself heard Anselm say.
All Gislebert's sons distinguished themselves, and the family proved generous benefactors to the Abbey of Bec.
Two of his descendants subsequently became monks there: Gilbert, afterwards Abbot of Westminster, who wrote the life of Herluin of Bec, founder and first Abbot of Bec; and his brother Milo.