Simultaneous electric field and plasma observations with the low‐altitude polar‐orbiting satellite Injun 5 have provided a comprehensive survey of convection electric fields and their association with magnetospheric plasma phenomena. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally antisunward convection poleward and sunward convection equatorward of the electric field reversal location. The electric field reversal is interpreted as the boundary between open and closed magnetic field lines. During local day the electric field reversal is observed to coincide with the equatorward boundary of the polar cusp. The plasma flow in the dayside polar cusp region is dominantly E‐W, away from the stagnation point, the convection velocities typically being ∼1 km sec−1. At local evening, ‘inverted V’ electron precipitation bands are observed near or at the position of the electric field reversal. In the local late‐evening sector the electric field reversal becomes less distinct, and often no single well‐defined electric field reversal can be identified. In all cases the inverted V electron precipitation events are closely associated with large, typically >30 mv m−1, irregular electric field fluctuations with time scales of a few seconds or less. Often these fluctuations comprise distinct ‘spikes’ of a few seconds duration or less, which can be identified with distinct boundaries or other features of the electron precipitation. In the local midnight sector, convection electric fields of >50 mv m−1 associated with plasma sheet electrons have been observed extending deep into the magnetosphere, equatorward of the electron (E > 45 kev) trapping boundary. These convection electric fields are characterized by considerably smaller fluctuations relative to those observed within the inverted V electron precipitation bands. To investigate the electric field and plasma interrelationships during a polar magnetic substorm, a series of passes obtained before and during a substorm is presented. Large antisunward convection velocities were detected over the polar cap several tens of minutes before the onset of the expansive phase of the substorm. These convection velocities gradually decreased during the decay phase of the substorm. Our measurements of enhanced antisunward flow over the polar cap region are generally consistent with several current ideas concerning the origin of substorms.