This paper explores the issues of integrating all the elements necessary to support a healthy and productive crew in a space habitat. The problem of this system integration hinges largely upon the nature of the structural system, both of the primary pressure envelope and the internal secondary structure of floors, partitions, hard points and stand-offs. This habitat integration must accommodate the life support system, stowage, private quarters, group activity areas, and working areas. The working areas may include laboratories, control centers, maintenance and repair facilities. Human factors engineering design stands as a challenge throughout the habitat.The distinction between an interplanetary habitat for zero gravity and a planetary surface habitat for a gravity field serves as an important design driver and discriminator. Environmental effects such as ionizing radiation, ultraviolet radiation, meteoroids, extremes of hot and cold act as determining factors as well. These requirements can be so demanding that they overshadow the specific objectives of particular human exploration missions. The means and methods of meeting these requirements raise the issue of what it means to build a lunar or planetary infrastructure for human habitation.