This article reports world averages for measurements of b-hadron, c-hadron, and τ lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available at least through the end of 2009. Some of the world averages presented use data available through the spring of 2010. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, and parameters of semileptonic decays.3 The DELPHI result of Ref. [25] is considered to supersede an older one [26]. 4 CDF updated their measurement of f baryon /f d [29] to account for a measured p T dependence between exclusively reconstructed Λ b and B 0 [31].