Intravascular ultrasound is a new method for visualizing the details of vascular pathology, providing high resolution images of plaque and thrombus. This review summarizes the potential applications of ultrasound imaging in the guidance of balloon angioplasty, atherectomy, laser ablation and stenting. Ultrasound differs from angiography and angioscopy in its ability to penetrate below the surface of the vessel lumen, demonstrating specific aspects about the distribution and composition of plaque. Because the different layers of the arterial wall have different acoustic properties, ultrasound catheters are able to define the layers of normal wall in comparison with plaque. Particularly in combination with therapeutic techniques designed to remove or ablate plaque, ultrasound may prove useful in maximizing the amount of plaque treated and minimizing trauma to normal vessel wall components. Combined imaging/therapeutic devices are in the pilot phase of development and show promise for enhancing the safety and efficacy of the catheter devices.