Security element 2, 4 to be embedded in or applied to a security document so that it is visually recognizable from both sides of security document 1 is of multilayer construction and includes interference element I with a color shift effect and diffraction structures 8. Depending on the arrangement of the layers and existing diffraction structures 8 on transparent substrate S the color shift effect and/or the diffractive effects are perceptible from one or both sides of security element 2, 4. The security element is suitable in particular as two-sided windowed thread 4 and as label or transfer element 2 over hole 3.