Radiopharmaceuticals are the main tool in nuclear medicine for diagnosis and therapy of human diseases. Development of new adiopharmaceuticals is based on the clever design of not only the carrier molecules guiding the drug to the target ells/organs but also majorly based on the physicochemical properties of the radionuclides. Beta and recently alpha mitters have become the major source of therapeutic energetic particles for developing therapeutic radiopharmaceuticals in the last three decades. However, availability, cost, stability of complexes as well as metallic/non-metallic properties of these radioisotopes play a major role in the field. On the other hand, development of new chelating agents with high affinity for various metallic radionuclides as well as room temperature labeling has emerged new series of therapeutic and/or diagnostic radiopharmaceuticals known as theranostics. The other major issue in this field is the agreement of physical half-life with the biological half-life to allow adequate targeting time and reducing the unwanted radiation ose and unspecific organ targeting.