A high energy electron beam monitor which detects the Cˇerenkov light emitted in nitrogen gas at atmospheric pressure is described. The monitor is designed to have a constant sensitivity to electrons of energies above 200 MeV, to have a response time of less than 10−7sec, and to have a current output which is linearly proportional to the beam intensity over a range of five decades. The results of tests made on the monitor are presented. The tests show that the monitor has a sensitivity, speed, range, and lack of dependence on beam position and background radiation which make it ideal for many monitoring applications.