The first chapter (236) in this volume of the Handbook on the Physics and Chem- istry of Rare Earth is a recapitulation of the scientific achievements and contri- butions made by the late Professor LeRoy Eyring (1919–2005) to the science of the lanthanide oxides in which the lanthanide element has a valence equal to or greater than three. Although LeRoy had a broad range of interests in the chemistry of the rare earths and actinides the main focus of his outstanding scientific career was concerned with the lanthanide higher oxides. This chapter was written by Dr. Zhenchuan Kang his last post doctoral associate. Professor Eyring was a.