Gallium-68 is of practical interest for clinical positron emission tomography (PET), a non-invasive imaging technique of high resolution, sensitivity and accurate quantification. The use of PET in nuclear medicine depends on the accessibility of imaging agents. Gallium-68 is suitable for complexation with chelators, either naked or conjugated to various molecules with potential for the development of agents for targeted, non-targeted and pre-targeted imaging. It is readily available from a 68Ge/68Ga generator and its chemistry is straightforward and amenable to automated and kit type production. Its decay mode and half-life provide high quality PET images and allow sequential repetitive examinations. The production of agents with high specific radioactivity might be of great benefit for clinical practice and may promote personalized medicine. The book presents techniques for the radionuclide production and labelling with high specific radioactivity, development of various imagingagents and their biological, clinical and technological applications. The importance of specific radioactivity is demonstrated and discussed.