Radiation therapy (RT) is an essential component of effective cancer care and is used across nearly all cancer types. The delivery of RT is becoming more precise through rapid advances in both computing and imaging. The direct integration of magnetic resonance imaging (MRI) with linear accelerators represents an exciting development with the potential to dramatically impact cancer research and treatment. These impacts extend beyond improved imaging and dose deposition. Real-time MRI-guided RT is actively transforming the work flows and capabilities of virtually every aspect of radiation therapy. It has the opportunity to change entirely the delivery methods and response assessments of numerous malignancies. This review intends to approach the topic of MRI-based RT guidance from a vendor neutral and international perspective. It also aims to provide an introduction to this topic targeted towards oncologists without a specialty focus in radiation therapy. Specialty implications, areas for physician education, and research opportunities are identified as they are associated with MRI-guided RT. The uniquely disruptive implications of MRI-guided RT are discussed and placed in context. We further aim to describe and outline important future changes to the specialty of radiation oncology that will occur with MRI-guided RT. The impacts on radiation therapy caused by MRI-guidance include target identification, radiation therapy planning, quality assurance, treatment delivery, training, clinical workflow, tumor response assessment, and treatment scheduling. In addition, entirely novel research areas that may be enable by MRI-guidance are identified for future investigation.