Lead-203 and actinium-225 are radioactive nuclides (types of radioactive atoms) of much interest to the nuclear medicine community. Lead-203 emits gamma radiation suitable for diagnostic purposes, and actinium-225 releases alpha radiation that can be used to kill cancer cells. Administering either of these radionuclides into the body requires the construction of metal-based radiopharmaceuticals, which are comprised of four parts: a radiometal, a bifunctional chelator, a linker, and a targeting vector. Currently, there are no fda-approved radiopharmaceuticals that contain lead-203 or actinium-225. Crucial to the establishment of such radiopharmaceuticals is the development of chelators that both sequester the targeted metal ion and remain coordinated while in the body. Consequently, much of my research has been dedicated to developing new chelators to target lead-203 or actinium-225. This seminar will compare the ability of several of these chelators to coordinate either of these radionuclides, as well as highlight chelator design features to help other chemists better target these two metals in the future.