A current monitor suitable for use with continuous or pulsed high energy electron beams is described. It functions by collecting slow secondary electrons emitted on passage of high energy electrons through a thin foil in vacuum. The secondary current is a linear function of primary current at average primary currents up to at least 120 &mgr;a (peak current density −150 ma/cm2), and is independent of energy at least in the range 6–30 Mev. With design modifications, the device should be capable of monitoring current at energies as low as 1 Mev with negligible beam absorption.