Mode-locked ring oscillators and ring amplifiers have been investigated experimentally and theoretically. Numerical solutions to the rate equations showed that nonlinear losses have to be introduced into the rate equations in order to explain the experimental observations. The theory yields operating conditions for mode locking in good agreement with the experiment. Application of this theory to ring amplifiers shows that very good control of the injected pulse energy and the pump power are required for efficient suppression of satellite pulses. Preliminary experimental results support our theoretical predictions.