This paper reviews the various basic concepts the suppression of jet noise through engine or nozzle design. The significant features of each concept are discussed in terms of simple jet-flow models which enable prediction of the noise-generation characteristics of the resulting jet flows. These jet noise-generation models, which are generally substantiated by existing data, are utilized to demonstrate optimum design trends and limits for future jet-engine designs. The results show that future jet engines can have significantly lower noise levels than current generation jets if noise becomes a major criterion for engine design at its inception. However, unless the noise-generation characteristics of the jet are considered at the earliest design stage, the possibilities for reduction of the eventual noise through nozzle modification are limited. [This work was supported by the U. S. Air Force under Contract AF33 (616)-5744.]