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Magnetic resonance (MR) imaging and ultrasound (US) imaging are complementary and synergetic noninvasive imaging modalities. US imaging is practically free of geometric distortion and provides high temporal resolution and direct visualization of acoustic obstacles. MR imaging offers excellent tissue contrast and a confirmed method for near-real-time thermometry. Their combination may help increase the intraoperative control and assessment in image-guided therapies. The added value of this dual-modality imaging would consist of a more complete description of the anatomy investigated, more accurate targeting, efficient motion tracking, and reliable immediate assessment of the therapeutic results. This chapter focuses on truly simultaneous US/MR technology integration and early applications. A prototype setup designed to clinical standards is described together with the preliminary evaluation of the hybrid imaging performance in the abdomen. In particular, the precision of image coregistration was assessed in healthy volunteers. Furthermore, a complex study investigated the thermal cavitation effects produced by radio-frequency ablations. Simultaneous US imaging/MR imaging acquisition permitted us to demonstrate that the latter effects induce subsequent magnetic-susceptibility-mediated errors in proton resonance frequency shift thermometry, both in ex vivo models and in patients treated for hepatic malignancies. The foreseen perspectives of the hybrid US imaging/MR imaging technique are included in the final section.