The present paper contains a brief overview of the studies of mode and wave
interaction in gyrodevices. The main part of it is devoted to the discussi
on of physical effects caused by mode interaction in the free-running and p
hase-locked gyrotron oscillators. Also, the problem of the stability of lar
ge-signal operation of gyro-forward-wave amplifiers with respect to excitat
ion of parasitic backward waves is discussed.