Coordinates: 45°27′8″N 3°18′14″E / 45.45222°N 3.30389°E / 45.45222; 3.30389

The Alagnon is a French river that starts in the Massif Central within the Regional Natural Park of the Volcanoes of Auvergne (French: Parc Naturel Régional des Volcans d'Auvergne) and that flows through the Auvergne-Rhône-Alpes region. It is a left tributary of the Allier.