We are using the techniques of neutron and x-ray powder diffraction to learn more about the driving forces for structural transformations in Pu metal. This research is currently being conducted in three areas: (1) understanding the low melting point of Pu, (2) measuring the intergranular stresses that arise in solid-solid phase transitions of Pu, and (3) determining whether the idiosyncratic crystal structures of Pu are stabilized by Pu atoms in different valence states at different crystallographic sites. ©2000 American Institute of Physics.