A spatial coherence diagnostic for measuring the spatial coherence of laboratory x‐ray lasers has been developed. The x‐ray laser beam illuminates a uniformly redundant array of slits, producing a partially coherent diffraction pattern which can be analyzed to yield the complex coherence factor for the x‐ray laser beam from a single x‐ray laser pulse. Measurements using x‐ray lasers at LLNL will be presented and discussed in detail. Results from experiments conducted in collaboration with the Rutherford x‐ray laser consortium to improve the spatial coherence of x‐ray lasers will also be discussed. A definition of a highly spatially coherent x‐ray laser based on simple physical arguments will be given. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W‐7405‐ENG‐48.