Carotid duplex ultrasound emerged in the 1970s, and in the subsequent decade it leapt rapidly from the bench to the bedside. While duplex velocity criteria were initially validated against carotid angiograms with good fidelity, the methods of measurement employed by pivotal carotid trials in the 1990s necessitated a revalidation of existing classification schemes. Today, there is significant variation in the criteria used by vascular laboratories, with early efforts towards standardization correlating poorly with other imaging modalities. The new Intersocietal Accreditation Commission modified consensus criteria revised in 2023 represent the newest effort to standardize duplex criteria based on traditional as well as more clinically relevant metrics. In the modern era, duplex ultrasound has shown benefit in screening asymptomatic groups at high risk for carotid stenosis such as those with numerous atherosclerotic risk factors, high-risk patients undergoing coronary artery bypass grafting, and those with lower extremity peripheral arterial disease. Carotid duplex also serves as a practical method of surveilling patients for restenosis after carotid endarterectomy and carotid artery stenting, with recent studies guiding modified velocity criteria in this population. Characterization of plaque morphology continues to evolve and may predict plaques at high risk of becoming symptomatic, and those which may respond poorly to carotid stenting. Even with the emergence of higher spatial resolution modalities such as CT and MR angiography, carotid duplex continues to play a critical role in the current diagnosis and treatment of carotid disease.