A method of Q-switching is described in which two Fabry-Perot etalons replace the output mirror of the laser resonator. The etalons behave as a variable output coupler and the system will Q-switch if the optical spacing of one of the etalons is changed sufficiently rapidly. A number of mechanisms which limit the hold-off power of the switch are discussed, and experiments with a continuously pumped Nd/YAG laser are reported. Repetitive Q-switching was demonstrated by changing the output etalon spacing with a piezoelectric transducer.