Curved surfaces particularly reflectors such as concave mirror elements for use in astronomical telescopes, solar energy concentrators etc., and methods of forming such surfaces. A rigid body with a curved surface is formed by providing a mould (20) having a curved surface with a curvature opposite to that of the required curved surface, applying a vacuum to the curved surface of the mould to deform a flexible, generally planar member (14) to match the curved surface of the mould and bonding a front surface of a structurally rigid base member (12) to the opposite surface of the planar flexible member while the vacuum is applied. Peripheral casing members (16, 18) may he bonded to the base member. The base member is formed from a rigid, low-density material such as an aluminium or aluminium alloy honeycomb material. The flexible (reflective) member may comprise a thin metallic sheet such as an anodised aluminium alloy sheet, and any casing members may also be of aluminium or aluminium alloy.