On the 2-primary v1-periodic homotopy groups of spaces A.K. Bousfield bous@uic.edu AMS Classification Numbers: 55Q51(Primary),55N15,55P60,55S25,57T20 We develop foundations of a general approach for calculating p-primary v1-periodic homotopy groups of spaces using their p-adic KO-cohomologies and K-cohomolgies with particular attention to the case p = 2. As a main application, we derive a method for calculating v1-periodic homotopy groups of simply-connected compact Lie groups using their complex, real, and quaternionic representation theories. This method has been applied very effectively by D.M. Davis in recent work. We rely heavily on the p-primary v1-stabilization functor Phi from spaces to spectra. Roughly speaking, we obtain the p-primary v1-periodic homotopy of a space X from the p-adic KO-cohomology of Phi X, which we obtain from the p-adic KO-cohomology and K-cohomology of X by a v1-stabilization process under suitable conditions.