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.