Throughout Europe and Asia, microsphere contrast agents called microbubbles are revolutionizing traditional ultrasonography, dramatically improving the precision of diagnostic sonograms and expanding the clinical scope of a widely used imaging modality. Microbubbles improve visualization of blood flow, the cardiovascular system and the perfusion of blood into vital organs, particularly the liver, making contrast-enhanced ultrasound (CEUS) competitive with other diagnostic imaging modalities for these applications. This article reviews the concepts, principles, applications and techniques of CEUS and describes changing regulatory views regarding contraindications. Emerging therapeutic applications also are discussed. This article is a Directed Reading. Your access to Directed Reading quizzes for continuing education credit is determined by your area of interest. For access to other quizzes, go to www.asrt.org/store.