Theoretical formulae are found for the reflection from flat sheets and angle reflectors. The reflection diagram from a flat sheet is the same as the transmission polar diagram of an aperture of double the dimensions of the sheet. A small deviation from flatness considerably alters the diagram, a sag of half a wavelength at the centre producing a zero where there would otherwise have been a maximum. The right-angled corner reflector is also investigated, and the broad reflection diagram expected from geometrical optics is found. The effect of a small departure of the included angle from a right angle is also discussed.