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The temporal evolution of the current, voltage and rf fields in magnetron-type devices has been simulated numerically by a two-dimensional, electromagnetic, fully relativistic particle-in-cell code. The simulation allows for the complete geometry of the anode vane structure, space-charge limited cathode emission, and the external power source. The code has been applied to mag-netrons operating in the relativistic energy regime.- 2-Unprecedented rf powers (-300MW to-3GW) have been achieved in elativistic magnetronsl-9 operating at voltages from several hundred kilovolts to 1MV, and drawing kiloamperes of current from field emission cathodes. These impressive results have reawakened an interest to better understand the interaction of the electro-magnetic field and the dense space charge cloud in magnetron-type devices. Numerous attempts have been made over a span of fort