The Illiac IV was the first large scale array computer. As the fore- runner of today's advanced computers, it brought whole classes of scientific computations into the realm of practicality. Conceived initially as a grand experiment in computer science, the revolutionary architecture incorporated both a high level of parallelism and pipe- lining. After a difficult gestation, the Illiac IV became operational in November 1975. It has for a decade been a substantial driving force behind the develooment of computer technology. Today the Illiac IV continues to service large-scale scientific aoolication areas includ- ing computational fluid dynamics, seismic stress wave propagation model- ing, climate simulation, digital image processing, astrophysics, numerical analysis, spectroscopy and other diverse areas. This volume brings together previously published material, adapted in an effort to provide the reader with a perspective on the strengths and weaknesses of the Illiac IV and the impact this unique computa- tional resource has had on the development of technology. The history and current status of the Illiac system, the design and architecture of the hardware, the programming languages, and a considerable sampling of applications are all covered at some length. A final section is devoted to commentary.