Adalhelm (died c. 910) was the bishop of Séez for twenty-six years starting around 884. He was a Benedictine monk and abbot at the abbey of Anisole.
Adalhelm wrote a life and miracles of Saint Opportuna of Montreuil, Vita et miracula Sanctae Opportunae. It includes an autobiographical account of how he was captured by Vikings in the year of his consecration and sold into slavery. It is the only first-hand account of a Viking slave. He escaped or was redeemed and returned to Séez, where he fulfilled a vow had made by writing the life of Opportuna. The Vita survives only in a 14th-century manuscript and an early modern edition.
Source: Adalhelm of Séez, from The Miracles of Saint Opportuna, 886–887