Extrapolation of the conventional diode equation into the oscillating region gives formal expressions for the internal and external efficiencies in terms of waveguide parameters, threshold current, and the voltage derivative of laser power. The latter, which depends on band and laser theory, is examined for two models. Linear perturbation theory gives qualitative conclusions which are of little utility for actual devices. Combination of diode analysis with the band theory of Stern and theP* theory of North gives a comprehensive theory of the current dependence of the static properties of the laser. The assumptions of the extrapolation are discussed, and experimental examples are presented to illustrate the utility of the new diode analysis. The comprehensive theory is used to interpret various known properties of devices such as linearity of power with current, change of internal efficiency with waveguide thickness, change of junction resistance at threshold, and several scaling laws. The types of experiments to test the theory are discussed and, in particular, the properties peculiar to theP* interaction. Many studies of the latter have shown its rather general applicability, but its utility for ’’pure mode’’ lasers with narrow spectra has not yet been thoroughly studied.