<div class="htmlview paragraph">Theories which have been proposed as an explanation of brake squeal are reviewed. It is now thought that disc brake squeal is best explained by modeling the brake as a multi-degree of freedom spring-mass system which may be stable or unstable depending on the values of its parameters.</div> <div class="htmlview paragraph">A method of testing disc brakes to measure squeal is described. Test results show that squeal is eliminated if the rotor is slotted. Test results also show that changes in friction material and pad contact geometry can have a significant effect.</div> <div class="htmlview paragraph">It is concluded that the elimination of disc brake squeal will require both better matching of the friction material to the brake, and improvements in the design of the brake.</div>