This paper presents a physical explanation of the phenomenon of low frequency oscillations experienced in power systems. A brief account of the present practice of providing fixed gain power system stabilizers (r, ss) is followed by a summary of some of the recent design proposals for adaptive PSS. A novel pss based on the effort of cancelling the negative damping torque produced by the automatic voltage regulator (AVR) is presented along with some recent studies on a multimachine system using a frequency identification technique.