The role which nuclear medicine (NM) imaging plays in the diagnosis of many diseases is already well recognized. In contrast to mostly anatomical modalities (CT, MRI and US), NM is able to provide in-vivo images examining functions of different body parts and organs. Additionally, recent years have witnessed a greatly increased interest in nuclear medicine applications in molecular imaging, targeted radiotherapy and “personalized-medicine” treatments. In my talk, I will introduce the basic principles of nuclear medicine, show examples of its most important clinical applications and discuss some of the latest advances. As any development in medical imaging requires involvement and close collaboration of scientists from many disciplines, the role and contributions of physics and physicists in different aspects of NM imaging will be discussed.