The Theodul Glacier (also spelled Theodule Glacier; , ) is a glacier of the Alps, located south of Zermatt in the canton of Valais. It lies on the Swiss side of the Pennine Alps, although its upper basin touches the Italian region of the Aosta Valley. The glacier descends from the west side of the Breithorn () and splits into two diverging branches above Gandegg: the Upper Theodul Glacier (Oberer Theodulgletscher), spilling on a high plateau near Trockener Steg, together with the Furgg Glacier, and the Lower Theodul Glacier (Unterer Theodulgletscher), reaching a height of about above the Gorner Glacier. Both branches are part of the Rhone basin, through the rivers Gornera, Mattervispa, and Vispa. Slightly above the glacier splitting is the Theodul Pass, crossing the border between Switzerland and Italy, and connecting Zermatt to Breuil-Cervinia. On the west, the Theodul Glacier is overlooked by the Matterhorn.