Europium is a chemical element with the symbol Eu and atomic number 63. Europium is a metal about as hard as lead and is quite ductile and is the most reactive of the rare earth elements. This book presents current research in the study of Europium including a review on the photoluminescence of the europium ion in different materials, organic europium complexes and their applications in organic light-emitting diodes and memory devices, europium compounds and their optical applications, and organic and inorganic emitting materials using Eu-Complex.