In this paper we review the current status of intravascular ultrasound. Data from qualitative and quantitative studies is presented. Our experimental findings and those of other investigators are reviewed. Intravascular ultrasound has been shown to delineate normal and abnormal arterial morphology as well as to identify and differentiate fibrous, lipid-rich, calcified plaques and complicated plaques. Quantitative studies show strong correlations between ultrasound and histology for lumen area, wall thickness, and plaque area. In vivo studies from our experimental work and clinical laboratory as well as the work of other researchers is presented. This data supports the potential of ultrasound imaging for guidance of intravascular intervention. The potential advantages and limitations of this new technology are discussed. This methodology shows promise for the assessment of the extent and severity of atherosclerosis, monitoring its progression and regression and guiding intravascular plaque ablation technologies.