Cancer, one of the leading causes of death worldwide, remains a challenge to treat. Over the last decades, targeted therapies have emerged as a way to selectively target and treat the affected cells, leaving the healthy ones intact. Nanomaterials, with their high surface area, ease of functionalization, and interesting physicochemical properties, are seen as promising carriers for therapeutic radionuclides. Their optical, electronic, and magnetic properties can be supplemented by the emitted ionizing radiation to form theranostic (therapeutic and diagnostic) or combined therapeutic agents. This review describes how different relevant therapeutic radionuclides can be incorporated into inorganic nanoconstructs to be delivered to the cancer cells and their impact on tumors. Different types of nanomaterials as well as multiple ways of incorporating radionuclides and their impact on the stability and both in vitro and in vivo performances are discussed.