The area of molecular imaging has matured over the past decade and is still growing rapidly. Many concepts developed for molecular biology and cellular imaging have been successfully translated to in vivo imaging of intact organisms. Molecular imaging enables the study of processes at a molecular level in their full biological context. Due to the high specificity of the molecular readouts the approach bears a high potential for diagnostics. It is fair to say that molecular imaging has become an indispensable tool for biomedical research and drug discovery and development today.