This monograph is a mathematical study of steady-state motions of a spinning hyperelastic incompressible, homogenous and isotropic cylinder. So far there was very little quantitative information on this subject and no mathematical analysis. The authors developed mathematical tools that are not standard in this kind of bifurcation problems. Qualitative results independent of the stress-strain relation are obtained that are consistent with physical experiments. These phenomena are shown to be related to mathematical bifurcation. The spectral analysis is accomplished by a new method that combines techniques of the modern theory of partial differential equations and abstract functional analysis with Fourier decomposition and sharper results on Bessel functions. These techniques represent in their own right a contribution that will find application not only in the study of rotating bodies, but in other physical situations that can be characterized by non-compact bifurcation.