  For an electrostatic wave interacting with a single species in a
collisionless plasma, momentum conservation implies current conservation.
However, when multiple species interact with the wave, they can exchange
momentum, leading to current drive. A simple, general formula for this driven
current is derived. As examples, we show how currents can be driven for
Langmuir waves in electron-positron-ion plasmas, and for ion-acoustic waves in
electron-ion plasmas.
