Bioluminescence methods are gaining increased attention due to their sensitivity, selectivity, and simplicity, along with the fact that bioluminescence can be monitored both in vitro and in vivo. This book introduces bioluminescence and fluorescence systems, along with the principles of their application for in vivo imaging of intracellular processes, and covers recent developments in optical (bioluminescence and fluorescence) imaging in cell biology. This book is intended for scientists and students involved in basic cell physiology research, as well as industry professionals, engineers, and managers involved in drug discovery and pre-clinical drug development. It discusses the practical aspects of luminescence in vivo imaging for monitoring intracellular processes. While some basic knowledge of biochemistry and biophysics is preferable, the book includes a brief review of fundamental principles to allow those not familiar with these disciplines to grasp basic concepts.