This volume of theHandbook on the Physics and Chemistry of Rare Earths adds three new chapters to the series, describing three different aspects of rare-earth science. The volume opens with an overview of the dual nature of 4f states in the lanthanides (Chapter 241). It is followed by a review of the temperature-dependent behaviors of aluminates and gallates, the structures of which are based on the simple, yet flexible, cubic perovskite model (Chapter 242).