Coronary angiography remains the standard technique for the assessment and therapy of coronary artery disease. Recently, intravascular ultrasound (IVUS) has emerged as a new adjunctive invasive tool which allows the acquisition of direct images of the atherosclerotic plaque in the cardiac catheterization laboratory; however it cannot be considered as an alternative to angiography. The aim of this article was to describe the indications, technique, and interpretation of IVUS imaging and its diagnostic and therapeutic applications, to review the pertaining literature and report the experience from our catheterization lab group. Ultrasound provides a unique method to study the regression or progression of atherosclerotic lesions in vivo. Lipid-laden lesions appear hypoechoic, fibromuscular lesions generate low-intensity or "soft echos" while the fibrous and calcified tissue impedes ultrasound penetration, obscuring the underlying vessel wall (acoustic shadowing). IVUS has been used to evaluate arterial remodeling: positive remodeling is the increase in arterial size to compensate for plaque accumulation and represents a compensatory mechanism to preserve lumen size; negative remodeling is vessel shrinkage and has been implicated in restenosis after balloon angioplasty. Positive remodeling seems to be significantly more frequent in myocardial infarction and unstable angina, negative remodeling occurs more often in stable coronary syndromes and is the main mechanism of restenosis after balloon angioplasty. In ostial and bifurcation lesion, the stenosis may be obscured by overlapping contrast-filled structures. Intermediate stenoses are particularly problematic in patients whose symptomatic status is difficult to assess. In these ambiguous situations, ultrasound provides a tomographic perspective, independent of the radiographic projection, which often allows precise lesion quantification. IVUS has emerged as the optimal method for the detection of diffuse post-transplant vasculopathy. Rapidly progressive intimal thickening (> 0.5 mm increase) in the first year after transplantation has major negative prognostic significance. The safety of IVUS is well documented, with studies reporting complication rates varying from 1 to 3%; the complications most frequently reported is transient spasm. Ultrasound allows us to evaluate plaque morphology, plaque eccentricity and lesion length, often helping in procedural decision-making. IVUS demonstrates plaque fracture and arterial wall dissection more often than angiography. Coronary angiograms frequently underestimate disease burden, whereas IVUS identifies residual plaque burden and minimal lumen diameter as the most powerful predictor of clinical outcome (restenosis). Several IVUS studies of directional atherectomy have addressed the issue of more aggressive plaque removal possibly resulting in decreased angiographic restenosis rate. IVUS imaging has played a pivotal role in the optimization of stent therapy. The concept of high-pressure stent implantation disseminated quickly, and larger trials demonstrated the safety of stent implantation using high pressures. IVUS has shown that in-stent restenosis is determined by the degree of intimal hyperplasia within the stent or in the stent border. In conclusion, the use of IVUS in the world is slowly increasing. Ultrasound commonly detects occult disease in patients with coronary artery disease. However, no short- or long-term studies have determined whether disease detected exclusively by ultrasound portends a worse prognosis as compared with "true normal" angiography.