Radiopharmacy is a pharmaceutical specialty responsible for the development and production of radiopharmaceuticals. Radiopharmaceuticals are radioactive drugs, which can be used in two distinct manners: first for diagnosis in oncological, neurological and cardiac diseases, and second for therapy in oncology. Given their great specificity and precision, radiopharmaceuticals are among the most technological products in the field of pharmacy. Among radiopharmaceuticals, radiopharmaceuticals based on Tc-99m are the most widely used in the world. However, radiopharmacy and radiopharmaceuticals are still restricted to a few research centers in the world today. This is largely due to the difficulty in obtaining the radioactive material, the precursor of the radiopharmaceutical, as well as the understanding of the chemistry involved in these materials. In this sense, this study addresses the radiochemistry of radiopharmaceuticals based on Tc-99m as well as the coordination chemistry of these compounds. Finally, this review addresses the pharmaceutical aspects of Tc-99m radiopharmaceuticals.