This book provides a comprehensive guide to the development, testing, and medical applications of photoluminescent materials. It covers key material classes-such as quantum dots, organic fluorophores, and lanthanide-doped nanoparticles-and explores how their light emission properties can be tailored for medical use. Readers will find in-depth discussions on biocompatibility strategies, targeted drug delivery with light-triggered release mechanisms, in vivo imaging for real-time therapeutic monitoring, and advanced diagnostic techniques like biosensors and fluorescence assays. The book also delves into photoluminescence-based therapies, including antibacterial treatments, photoimmunotherapy, and cancer phototherapy, offering researchers and practitioners the tools to develop safe and effective next-generation medical technologies.