This chapter tackles positron emission tomography (PET), a functional neuroimaging technique that revolutionized brain imaging in the 1970s by providing the first colorful maps of brain activity. Beginning with its historical development from Hans Berger’s early hemodynamic measurements to modern scanners, the chapter examines how PET visualizes metabolic processes by tracking radioactively labeled tracers in the bloodstream. Unlike structural imaging methods, PET detects gamma rays emitted when positrons from the radiotracer collide with electrons, allowing researchers to measure regional changes in blood flow, glucose metabolism, and neurotransmitter activity related to cognitive processes. The chapter details practical aspects of PET studies, including experimental design, data acquisition, image reconstruction techniques, and visualization methods like subtraction analysis for mapping task-related brain activity. While MRI-based techniques have supplanted PET for many cognitive neuroscience applications, PET remains invaluable for certain investigations due to its unique ability to label diverse compounds, particularly for studying neuropsychiatric disorders, neurotransmitter systems, and metabolic processes in diseases like Alzheimer’s and epilepsy.