Today’s cerebral vascular physiologists have a variety of techniques available to measure cerebral blood flow (CBF) and assess cerebral vascular reactivity. CBF measurement techniques can be grouped based on anatomical considerations (e.g., local, regional, global), number of measurements permitted (e.g., single, multiple, continuous), and/or the types of data provided (e.g., images, absolute vs. relative CBF values). In addition to the methods that measure CBF, others are designed to measure the responses of individual or groups of cerebral arteries to changes in intravascular pressure or extracellular oxygen or carbon dioxide levels (e.g., cranial windows, isolated arterial segments). However, since each of these myriad techniques has advantages and limitations, investigators must choose the most appropriate based on when and where they want to measure cerebral vascular function. This chapter provides a brief discussion of the physiological principles on which the majority of CBF measurement methods are based as well as descriptions of the advantages and disadvantages of the methods most often used in the current measurements of cerebral vascular function and dysfunction after traumatic brain injury.