The methods of calculating fields due to quasi-steady currents in closed and unclosed circuits are reviewed. It is emphasized that it is sufficient to apply the Biot-Savart law to all the moving charges and to ignore the vacuum displacement current. Attention is drawn to a basic error in the widespread practice of treating a circuit containing a capacitor as though the fringing fields could be ignored and the displacement current replaced by conduction currents confined to the gap between the plates.