The measurement of elastic moduli can provide crucial input to fundamental descriptions of the electronic structure and thermodynamics of Pu because elastic moduli play a leading role in determining how thermal energy is distributed among internal vibrations, which, for the most part, control the entropy at ambient temperatures and above. In addition, elastic moduli are important parameters for engineering processes related to the fabrication and function of Pu components and are often the most sensitive of physical parameters to changes in material properties with age, composition or temperature. We describe here the rationale, techniques, and results for recent studies of the elastic moduli of Pu. ©2000 American Institute of Physics.