<div class="htmlview paragraph">This paper describes a variety of methods employed in the past to modify or suppress jet noise. Some of the intriguing aspects of the factors that contribute to noise suppression are brought out. The paper concludes that a systematic study of the physics of jet suppression, in place of the ad hoc methods used in the past, is required if the concepts involved are to be utilized for design and accurate predictions in the quest for the quiet aircraft.</div>