Stimulated emission of synchrotron radiation is possible when an electromagnetic wave polarized in the orbit plane propagates across a static magnetic field along which relativistic electrons gyrate. In principle, optical gain can be observed up to gyration harmonic numbers n of the order of ncr equals 3γ3, where γ is the relativistic energy factor. For n > ncr the gain falls off as exp(-2n/ncr). A universal gain formula is presented, valid for all values of n/ncr. It is shown that synchrotron radiation laser (SRL) gain is large than FEL gain when a similar electron beam is considered. For millimeter wavelength SRLs at 100 and 300 GHz, conceptual designs are presented which use a 2 MeV sub-Ampere electron beam with a magnetic field as low as 6 kG. For shorter wavelength SRLs, including visible wavelength devices, beam cooling may be required to obtain the necessary low energy spread. A means for achieving the cooling is described. A conceptual design for a 633 nm SRL is presented which would use a 10 MeV, 0.2 Ampere beam in a 100 kG uniform magnetic field.