At the outset of a saturation diving mission, a selection of the basic diving system to safely accomplish the tasks involved must be made. The main components, deck decompression chamber (DDC) and submersible decompression chamber (SDC), are designed as conventional pressure vessels, though special attention is now being given to hatches, viewports, and electrical penetrations due to constraints imposed by personnel habitation requirements. Where divers have to be transferred between chambers under pressure, a reliable chamber mating system is essential. A rationale is offered for the design of such critical components as the SDC umbilical and high-pressure breathing gas storage and distribution systems. In the water, diver safety is very much dependent upon the face mask. The development of an optimum full-face mask, incorporating hard wire communication, is described. In conclusion, human engineering and psychological considerations are presented. These offer to show how the designer can have a significant influence on the state of mind of the diver and operator arid make both safer on the job.