Magnetic resonance imaging (MRI)-based monitoring has been shown in recent years to enhance the effectiveness of minimally or noninvasive thermal therapy techniques, such as laser, radiofrequency, microwave, ultrasound, and cryosurgery. MRI's unique soft-tissue contrast and ability to image in three dimensions and in any orientation make it extremely useful for treatment planning and probe localization. The temperature sensitivity of several intrinsic parameters enables MRI to visualize and quantify the progress of ongoing thermal treatment. MRI is sensitive to thermally induced tissue changes resulting from the therapies, giving the physician a method to determine the success or failure of the treatment. These methods of using MRI for planning, guiding, and monitoring thermal therapies are reviewed.