To present the development of a compact low field intraoperative MR image guidance system and its application in brain surgery. The PoleStar ioMRI system (Odin Medical Technologies, Israel and Medtronic, Inc. USA) was developed for use in a standard operating room. Its primary physical fixed parameters are magnetic field of 0.15 T and field of view of 20 x 16 cm. The magnet is mounted on a transportable gantry and can be positioned under the surgical table when not in use for scanning. Additional functionality includes integrated navigation, and system operation by the surgeons. The PoleStar system integrates into existing operating rooms requiring only slight modification of the surgical environment. Standard instruments can be used. The system's imaging allows it to be used for the following indications: pituitary tumors, low grade gliomas (including awake surgery), high grade gliomas, intraventricular tumors, accurate navigation to small lesions such as cavernous angiomas or metastases, drainage of cysts and brain abscesses. The image quality, which is comparable to post operative diagnostic high field imaging, enables high quality resection control. More than 6,000 brain surgeries were done with the system in 50 centers in the US and Europe. The low field intraoperative MRI system is a valuable tool in the modern operating room.