"The , which measures the , together with the total energy density of the Universe, sets the size of the observable Universe, its age, and its radius of curvature. Excellent progress has been made recently toward the measurement of the Hubble constant: a number of different methods for measuring distances have been developed and refined, and a primary project of the has been the accurate calibration of this difficult-to-measure parameter. The recent progress in these measurements is summarized, and areas where further work is needed are discussed. Currently, for a wide range of possible s, the Universe appears to have a . Combined with current estimates of stellar ages, the results favor a . They are consistent with either an , or a with a non-zero value of the ."