The human brain burns up to 20 times the fuel of any other organ in the body, and glucose is virtually the only fuel it uses. Since no glucose store exists in the brain, the dependence that this organ shows on a continuous blood supply is total. This, along with the need to shield the microenvironment for brain activity, determines some unique anatomical and functional features of the cerebrovascular bed. From the anatomical point of view the following are worth mentioning: aterio-arterial anastomoses (collateral flow), macro- and microcirculation (from the circle of Willis to capillaries), histology of cerebral arteries (specifically the blood-brain barrier), and the "neurovascular unit" (endothelium-astrocyte-neuron link). As to the functional features one must take into account rheology (physical characteristics of the blood flowing through the cerebrovascular bed), venous drainage, and factors influencing cerebral vascular resistance and then regulating cerebral blood flow (CBF) (mechanical, metabolic, humoral and neural factors). Impairment of one or various of the mentioned factors can lead to dysfunction of the cerebral circulation. Impaired CBF seems to be on the basis of neurological disorders such as deterioration of cognitive function, Alzheimer disease or dementia; hypoperfusion of the cardiovascular control centres in the brainstem has been suggested as the cause of essential hypertension; etc. May be more importantly, acute reduction of CBF below the needs of the cerebral tissue (cerebral ischemia) affects to almost every factor mentioned above. If maintained, cerebral ischemia produces neuronal death. When such a situation comes from the occlusion (atherosclerotic or thrombo-embolic) of a cerebral artery (ischemic stroke), the affected tissue consists of a densely hypoperfused destined-to-die zone (infarct core), and a peripheral zone with a relatively well-preserved perfusion (ischemic penumbra). At the present time, therapeutic interventions to lysate blood cloth (thrombolysis) and to protect the tissue at risk in the ischemic penumbra (neuroprotection), offer the best opportunities to lower the impact of ischemic stroke.