A mirror (10, 20, 30, 40), more particularly for a microlithographic projection exposure apparatus, has an optical effective surface (10a, 20a, 30a, 40a), a mirror substrate (11, 21, 31, 41) and a reflection layer stack (14, 24, 34, 44) for reflecting electromagnetic radiation impinging on the optical effective surface (10a, 20a, 30a, 40a), wherein a layer (13, 23, 33, 43) composed of a group III nitride is arranged between the mirror substrate (11, 21, 31, 41) and the reflection layer stack (14, 24, 34, 44), wherein the group III nitride is selected from the group containing gallium nitride (GaN), aluminum nitride (AlN) and aluminum gallium nitride (AlGaN).