An air ionizer (10) has at least two electrodes (26) contained within a recessed region (18) of an insulating housing (12). When high voltages are applied to the electrodes (26), nearby air molecules are ionized and generally move towards a target region outside the housing (12). Because the insulating housing shields the electrodes (26) the production of ions is not significantly disturbed by charged or grounded objects other than those in the general direction of the target region. In one embodiment, the electrodes (26) are placed close enough to the inner walls of the recessed region (18) that the portions of the surfaces of the walls near the electrodes (26) are electrostatically charged. This charge tends to repel the nearby ions, expelling many from the recessed region (18) towards the target region.