This volume contains a collection of papers presented at the NATO Advanced Study Institute on ·Testing and Diagnosis of VLSI and ULSI" held at Villa Olmo, Como (Italy) June 22 -July 3,1987. High Density technologies such as Very-Large Scale Integration (VLSI), Wafer Scale Integration (WSI) and the not-so-far promises of Ultra-Large Scale Integration (ULSI), have exasperated the problema associated with the testing and diagnosis of these devices and systema. Traditional techniques are fast becoming obsolete due to unique requirements such as limited controllability and observability, increasing execution complexity for test vector generation and high cost of fault simulation, to mention just a few. New approaches are imperative to achieve the highly sought goal of the • three months· turn around cycle time for a state-of-the-art computer chip. The importance of testing and diagnostic processes is of primary importance if costs must be kept at acceptable levels. The objective of this NATO-ASI was to present, analyze and discuss the various facets of testing and diagnosis with respect to both theory and practice. The contents of this volume reflect the diversity of approaches currently available to reduce test and diagnosis time. These approaches are described in a concise, yet clear way by renowned experts of the field. Their contributions are aimed at a wide readership: the uninitiated researcher will find the tutorial chapters very rewarding. The expert wiII be introduced to advanced techniques in a very comprehensive manner.