PET imaging of integrin alpha-v-beta-3 expression has been studied intensely by the academia and recently also by the industry. Imaging of integrin alpha-v-beta-3 expression is of great potential value, as the integrin alpha-v-beta-3 is a key player in tumor metastasis and angiogenesis. Therefore PET imaging of this target might be a suitable in-vivo biomarker of angiogenesis and metastatic potential of tumors. In this manuscript, the various strategies for PET imaging of the integrin alpha-v-beta-3 will be summarized, in-cluding monomeric and multimeric radiolabelled RGD peptides and nanoparticles. While most experiments have been performed using preclinical tumor models, more and more clinical results on PET imaging of alpha-v-beta-3 expression are available and will be discussed in detail. However, while a multitude of radiotracer strategies have been successfully evaluated for PET imaging of alpha-v-beta3, the ultimate clinical value of this new imaging biomarker still has to be evaluated in large clinical trials.