The Hubble constant and new discoveries in cosmology

We report the outcome of a 3-day workshop on the Hubble constant (H_0) that took place during February 6-8 2012 at the Kavli Institute for Particle Astrophysics and Cosmology, on the campus of Stanford University. The participants met to address the following questions. Are there compelling scientific reasons to obtain more precise and more accurate measurements of H_0 than currently available? If there are, how can we achieve this goal? The answers that emerged from the workshop are (1) better measurements of H_0 provide critical independent constraints on dark energy, spatial curvature of the Universe, neutrino physics, and validity of general relativity, (2) a measurement of H_0 to 1% in both precision and accuracy, supported by rigorous error budgets, is within reach for several methods, and (3) multiple paths to independent determinations of H_0 are needed in order to access and control systematics.