Recent technological advances have made deep fast optical surveys of large fractions of the sky feasible. LSST is the exemplar. An 8.4m primary mirror with a 10 square degree field of view instrumented by a 3.2 Gigapixel CCD will survey more of the optical universe in one month than all previous telescopes. This will enable astronomical and fundamental physics investigations of the solar system, Milky Way, the transient sky and establish tight constraints on dark energy models. The major features and challenges will be described.