Recent measurements of the velocity of electromagnetic waves involving simultaneous high‐precision determinations of the frequency and wavelength of highly monochromatic radiation sources are reviewed. After an account of the frequency stabilization of lasers using Lamb‐dip and saturated molecular absorption techniques, the recent measurements of visible and infrared frequencies at NBS (Gaithersburg), NBS (Boulder), and NPL (Teddington) are discussed. The resulting experimental values for the velocity of lightinvacuoare summarized, and the remarkable improvement in our present knowledge ofcobtained from these laser measurements is indicated. The article concludes with a discussion of the suggestion that the velocity of light should be made a defined constant and of the effect such a definition would have on future light‐velocity measurements.