In most aspects of our lives, people encapsulate themselves in enclosures of one kind or another to provide separation and protection from local harsh environments, i.e., temperature, weather, fire, air flow, air pressure, etc., and to provide privacy and protection from predators. This encapsulation also provides some degree of protection from noise---often more by accident than design, for structural noise reduction is not always at the top of the list of design priorities. In order to provide adequate protection from noise for people and sensitive equipment in enclosed spaces, it is necessary to work within the design constraints imposed by the harsh environments. In many cases, this means that a rudimentary understanding of sound transmission through structures is not sufficient to achieve the necessary protection, and more advanced techniques are required. This tutorial will provide an overview of the principles of sound transmission through materials, highlighting some of the more common misconceptions, and presenting the design of structures for special applications. Examples will be given of the techniques and designs used in the expanding market for the sound insulation of buildings exposed to aircraft noise.