Abstract It has been confirmed that the mechanism of identation proposed by Hill et al. (1947), for the indentation of a plane surface by a wedge, operates when the wedge semi-angle is less than about 30°. If the wedge angle is greater than 30° a different mechanism appears and becomes progressively more important with increasing wedge angle. This mechanism approximates to a radial compression centred close to the line of first contact of the wedge. Indentation by conical and pyramidal indenters having an apex semi-angle of 68° also approxmates to a radial compression which produces hemispherical surfaces of constant strain centred close to the first point of contact between the indenter and the specimen. With blunt indenters, variations in the indenter shape cause very little difference in the deformation mechanism except, perhaps, in a highly deformed region close to the indenter.