Single photon emission computed tomography (SPECT) is obtained by the injection of one of a series of compounds that cross the blood-brain barrier and are distributed in the brain according to regional perfusion or to the density of a given receptor. The regional brain distribution of the injected compound can be measured because it is bound to a radioactive substance that emits photons. Emitted photons are collimated to facilitate determining their source and detected with sodium iodine crystal detectors. Finally, the techniques of CT are used to reconstruct the density of photons emitted by each volume element (voxel) of the brain. Less expensive and more widely distributed in nuclear medicine departments than positron emission tomography, SPECT is currently used mainly in the evaluation for epilepsy surgery, of cerebrovascular disease, and of the parkinsonian and other neurodegenerative syndromes. In this article, we discuss the technological aspects of brain SPECT and its clinical neurological applications.