A simple analytical model of frequency-modulation (FM) laser operation is proposed in terms of a master equation time-domain description. The analysis is capable of capturing the main experimental features of FM oscillation, including the dependence of modulation depth on cavity parameters, distortion effects induced by finite cavity gain bandwidth, and transition to FM mode-locking operation. Experimental results for a FM erbium–ytterbium–glass laser show good agreement with the theoretical predictions. ©1998 American Institute of Physics.