Peptide Receptor Radionuclide Therapy (PRRT) is an established treatment for non-operable or metastatic neuroendocrine neoplasms that express highly and frequently somatostatin receptors. More generally, PRRT is an attractive therapy option for delivering cytotoxic radiation to tumor cells through specific binding of a radiolabeled peptide to a molecular target. The development of imaging companions gave rise to the concept of radiotheranostics, important for in vivo tumor detection, characterization, staging but also, and more importantly, for individual patient selection and treatment. The success of somatostatin receptor targeting paved the way for the clinical translation of other peptide-based radiopharmaceuticals targeting, e.g. the receptors Cholecystokinin 2, Gastrin Releasing Peptide (GRPR), Neurokinin-1 and C-X-C motif chemokine 4 (CXCR4). While historically the Auger emitter ¹¹¹ In and the high-energy β- emitter ⁹⁰ Y were used, the vast majority of PRRT are currently performed with the medium-energy β- emitter ¹⁷⁷ Lu, while α emitters are increasingly studied in various clinical applications.