This book provides in-depth aspects of nanotechnology of rare earth (RE) materials. It starts with a review on the physical and chemical properties of RE elements, followed by a discussion on various strategies in fabricating nanosized RE materials. It describes various techniques in derivatizing surface molecules onto nanosized RE materials. A considerable portion of the book is devoted to the review and discussion of the application of nanosized RE materials as contrast agents in in vitro and in vivo fluorescence imaging, MRI, and integrated modalities imaging. The book also discusses the application of RE nanomaterials in LEDs.