The European Space Agency ESA is currently planning its next cornerstone mission of the Horizon 2000 space science programme, which is the high throughput x-ray astronomy mission XMM. The heart of the scientific payload consists of a set of 3 highly nested Wolter type I telescopes. A review of the optical design and layout is given. The grazing incidence mirrors will be made by epoxy replication on CFRP from a highly polished glass mandrel. This technique has been used to produce flat mirror samples, of which x-ray measurements of reflectivity and scattering are presented.