This standard describes the use of transmission Fresnel zone plates as lenses for X-rays. The physical principles are explained briefly. The typical parameters of Fresnel zone plates which are important for X-ray optics are elaborated on. The determination of these parameters by measurements is described in detail. The main applications are X-ray microscopy and X-ray spectral microscopy. This standard addresses users, developers and manufacturers of X-ray microscopes using transmission zone plates for imaging and focussing.