[v] This document describes the result of the work of several thousand engineers and scientists who, over the last ten years, have conceived, designed, developed, built, and tested Skylab, the most complicated space system in the American space flight program so far. As we are completing our writing just a few months before the launching of Skylab, we extend our appreciation and gratitude to all of those who have supported us in writing this booklet. Members of many organizations at NASA Headquarters in Washington, at the Lyndon B. Johnson Space Center, the Goddard Space Flight Center, the John F. Kennedy Space Center, and the George C. Marshall Space Flight Center have provided valuable advice and help. The Life Sciences Directorate at the Lyndon B. Johnson Space Center and the Office of Life Sciences at NASA Headquarters made substantial contributions to the chapter on Life Sciences Projects. Dr. G .C. Bucher, M. I. Kent, and R. M. Nicholson of the G. C. Marshall Space Flight Center were responsible for organizing the material and composing most of the booklet in its present form.