The thermal expansion of uranium and the nature of allotropic transformation processes in uranium are of obvious interest in predicting or understanding the effects of thermal cycling on components fabricated of uranium such as nuclear fuel elements. Quite apart from this possible immediate practical interest is the theoretical interest in the transformation processes themselves. The purpose of the investigation reported was to determine the temperature dependence of the lattice parameters of uranium from room temperature to the melting point and to provide experimental data on the general characteristics and kinetics of the allotropic transformations in uranium.