The rare earths play a unique role in science. These 17 related elements afford a panoply of subtle variations deriving from the systematic development of their electronic configurations, allowing a test of theory with excellent resolution. In contrast they find widespread use in even the most mundane processes such as steel-making, for polishing materials and gasoline cracking catalysts. In between are exotic uses such as TV screen phosphors, lasers, high strength permanent magnets and chemical probes. The multi-volume book, "Handbook on the Physics and Chemistry of Rare Earths", covers the entire rare earth field in an integrated manner. Each chapter is a comprehensive up-to-date, critical review of a particular segment of the field. The work offers the researcher and graduate student, alike, a complete and thorough coverage of this field. Volume 19 is the third volume of a three-volume set of reviews devoted to the interrelationships, similarities, differences and contrasts of the lanthanide and actinide series of elements. It comprises five chapters on the comparative physics and thermodynamics of the lanthanide and actinide materials. The first two chapters are concerned with neutron scattering studies, while the next two are concerned with physical property studies involving electronic, thermal and magnetic behaviours. The first chapter compares the inelastic neutron scattering behaviours of the lanthanides and actinides. The next chapter concentrates on neutron scattering by heavy fermion single crystal materials, including metallic and semiconducting antiferromagnets and nearly insulating paramagnets. Chapter Three, probably the most extensive and comprehensive one in the entire series, reviews intermediate valence and heavy fermions in a wide variety of lanthanide and actinide compounds, ranging from metallic to insulating materials. Chapter Five focuses on two issues on the high pressure behaviours of anomalous cerium, ytterbium and uranium compounds. The final chapter is an extensive review of the thermodynamic properties of lanthanide and actinide metallic systems.