Simple SummaryMagnetic resonance-guided radiotherapy (MRgRT) is an emerging radiotherapy technology combining real-time magnetic resonance imaging and radiation delivery. By administering radiation with a linear accelerator with built in low-field or high-field MRI, practitioners have a greater ability to align to the target for daily set-up, precisely track the motion of and thereby target or avoid tissues and adapt to inter-treatment daily changes. This decreased uncertainty has implications for facilitating smaller, less-toxic treatment margins, potentially allowing delivery of higher dose radiotherapy that will lead to better control of tumors. The technology has already found success in treating breast, prostate, pancreatic, liver, lung, and limited metastatic cancers, in addition to non-oncologic indications such as cardiac ablation. The present narrative review aims to describe the current and future state of MRgRT technology and research.AbstractMagnetic resonance-guided radiotherapy (MRgRT) represents a promising new image guidance technology for radiation treatment delivery combining an onboard MRI scanner with radiation delivery technology. By enabling real-time low-field or high-field MRI acquisition, it facilitates improved soft tissue delineation, adaptive treatment, and motion management. Now that MRgRT has been available for nearly a decade, research has shown the technology can be used to effectively shrink treatment margins to either decrease toxicity (in breast, prostate cancer, and pancreatic cancer) or facilitate dose-escalation and improved oncologic outcomes (in pancreatic and liver cancer), as well as enabling indications that require clear soft tissue delineation and gating (lung and cardiac ablation). In doing so, the use of MRgRT has the potential to significantly improve the outcomes and quality of life of the patients it treats. The present narrative review aims to describe the rationale for MRgRT, the current and forthcoming state of technology, existing studies, and future directions for the advancement of MRgRT, including associated challenges.