Radiotheranostics is a field of rapid growth with some approved treatments including 131 I for thyroid cancer, 223 Ra for osseous metastases, 177 Lu-DOTATATE for neuroendocrine tumors, and 177 Lu-PSMA (prostate-specific membrane antigen) for prostate cancer, and several more under investigation. In this review, we will cover the fundamentals of radiotheranostics, the key clinical studies that have led to current success, future developments with new targets, radionuclides and platforms, challenges with logistics and reimbursement and, lastly, forthcoming considerations regarding dosimetry, identifying the right line of therapy, artificial intelligence and more.