The four LEP experiments have each performed precision measurements of Z⁰ parameters. A method is described for combining the results of the four experiments, which takes into account the experimental and theoretical systematic errors and their correlations. We apply this method to the 1989 and 1990 LEP data, corresponding to approximately 650 000 Z⁰ decays into hadrons and charged leptons, to obtain precision values for the Z⁰ parameters. We use these results to test the standard model and to constrain its parameters.