Background: Theranostic procedures shape diagnostic and therapeutic patient care in nuclear medicine. This article presents advancements in established and new theranostic approaches at various clinical stages. Methods: The work is based on a compilation of recent literature and guidelines on the current status of the selected radiopharmaceuticals. Results: Radiopharmaceuticals for treatment of prostate carcinoma and neuroendocrine tumors have been approved for several years, both for diagnostics using positron emission tomography (PET) and for radiopharmaceutical therapy. For these established radiopharmaceuticals, clinical studies are currently underway on earlier use during the course of disease, combination therapies, new indications and the use of alpha emitters such as [²²⁵Ac]actinium instead of the beta emitter [¹⁷⁷Lu]lutetium. Radiolabeled CXCR‑4 ligands are radiopharmaceuticals for the receptor-specific detection and therapy of tumors with expression of chemokine receptor 4. Initial studies in hematological neoplasms such as non-Hodgkin’s lymphoma and multiple myeloma suggest that these radiopharmaceuticals will be used more frequently in the future. Other radiolabeled ligands, e.g., against the fibroblast activation protein (FAP) or for imaging hypoxic tissue, are currently opening up completely new opportunities for specific PET-based imaging of the tumor microenvironment. Conclusion: Following the approval of Lutathera® and Pluvicto®, studies are currently underway to explore extended and new indications for these radiopharmaceuticals. In addition, the alpha emitter [²²⁵Ac]actinium is also being investigated as an alternative therapeutic radionuclide. Other promising new theranostic agents for the diagnosis and systemic treatment of tumors are currently being investigated in clinical trials.