The W. M. Keck Observatory is a joint project of the University of California and the California Institute of Technology to build and operate a new ground-based astronomical telescope. The telescope will be used for observations at both visible and infrared wavelengths. One innovative feature of the telescope is the ten meter diameter primary, mirror (76m2). The mirror is a mosaic of thirty-six hexagonal segments. The fabrication of this large mirror requires 1) fabrication of the individual segments, 2) support of the segments, and 3) active control of the pistons and tilts of the segments. The glass-ceramic segments are 75mm thick and 1.8m in diameter. They will be polished using the technique of Stressed Mirror Polishing. First forces and moments are applied around the edge of the blank to deform the surface. Next a sphere is polished into the stressed blank. Finally the forces and moments are released and the blank elastically deforms to the desired off-axis section of a paraboloid. In the telescope, the segments are supported by whiffietrees which take axial loads and by a post attached to the center of mass with a thin diaphragm which takes radial loads. The relative pistons and tilts of the segments are electronically stabilized by an active servo system. We describe the status of the design and development work and the plans for fabrication.