The Optical Frequency Comb concept and technology exploded in 1999-2000 from the synthesis of advances in independent fields of Laser Stabilization, UltraFast Lasers, and NonLinear Optical Fibers. The Comb was developed first as a method for optical frequency measurement, enabling a thousand-fold advance in optical frequency measurement, and searches (in the 16th digit) for time-variation of physical "constants". The Comb methods also empower enhanced time-domain control, with broad applications in spectroscopy, metrology, and the extension of nonlinear optics into the XUV range and beyond. A comb-excited Cavity Ringdown measurement allows massively multiplex spectroscopy, sensitively to detect disease-marker molecules within human breath. In Comb-based length metrology, the incredible resolution is accessible ALONG WITH intrinsic resolution of the integer fringe question: two great applications will be control/calibration of next-generation interferometric planet-finder missions, and cold-start dimensional metrology for accurate photolithography of large semiconductor wafers.