Organic europium complexes are of considerable interest due to their sharp narrow emission spectrum and potentially high emission quantum efficiency, originated from 2D0-7F2 electronic transitions of the central ions. Therefore, organic europium complexes have well applications in organic light-emitting diodes. Furthermore, organic europium complexes also show well electrical switching characteristics in diodes, potential applications as memory devices in information storage. This book reviews the achieved progresses in organic europium complexes and their applications in organic light-emitting diodes and memory devices.