An extensometer has been developed to continuously monitor roof extension in underground mines. The extensometer is designed to be installed in the MSHA-mandated test holes in the roof and measures the displacement between an anchorage point at the top of the borehole and the hole in the roof of the excavation. Once installed, the extensometer will report displacement through semi-wireless communications network. The extensometer is hard-wired into the permissible MIDAS datalogger, where results can be obtained wirelessly via the MIDAS user interface. Lab tests have indicated that the device produces displacement data. The device was installed in one underground coal mine to review its effectiveness in the field. / Master of Science