When the performance envelope for the pressurized Navajo was finalized, it was apparent that a sophisticated environmental system was needed to guarantee passenger comfort. The environmental studies centered around the ventilation, pressurization, heating, and air cooling systems. This paper discusses parameters that governed the selection of each system design, and how they were intergrated into a proper functioning overall system. The hardware that was needed together with those factors that govern their selection are also discussed.Development of the various systems imposed many problems and the solution to these problems required many changes. Some of the more important of these are described in detail.