Transcranial Doppler ultrasonography (TCD) is the only diagnostic modality that provides a reliable evaluation of intracranial blood flow patterns in real-time. The physiological information obtained from TCD is complementary to the anatomical details obtained from other neuroimaging modalities. TCD is relatively cheap, can be performed bedside, and allows monitoring in acute emergency settings. TCD criteria for intracranial stenosis have been validated against various forms of angiographic studies and serve as reliable tools for screening, diagnostic as well as follow up purposes. TCD findings of intracranial stenosis have acceptable accuracy parameters for anterior as well as posterior circulation. Extended applications of TCD, especially emboli monitoring and assessment of vasomotor reactivity, provide important information about the pathophysiology of cerebrovascular ischemia and risk stratification. Therefore, TCD has become an integral component of the armamentarium of stroke neurologists for understanding stroke etiopathogenesis, planning and monitoring definitive treatment and determining the prognosis. We present the basic principles of TCD, techniques of test performance, diagnostic methods as well as some of the advanced applications of TCD in patients with intracranial stenosis.