Introduction Functional neuroimaging techniques used to study narcolepsy include single-photon emission computed tomography (SPECT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). SPECT shows the distribution of radioactive isotopes, the decay of which is associated with the emission of detectable single gamma photons. Examples of SPECT isotopes are technetium-hexamethylpropylene amine oxime (Tc-HMPAO) and technetium-ethyl cysteinate dimer (Tc-ECD), both indirect markers of regional cerebral blood flow (rCBF). PET shows the distribution of compounds labeledwithpositron-emitting isotopes, suchas [O]-labeledwater (H2 O), an indirect marker of rCBF, and F-fluorodeoxyglucose (F-FDG), amarker of glucosemetabolism (CMRglu). Functional MRI measures the variations in brain perfusion related to neural activity, using a method based on the assessment of the BOLD (bloodoxygen level-dependent) signal. SPECTandPETcan alsobe coupled with synthetic ligands to specific receptors of interest, in order to investigate neuromodulatory changes associated with a condition. In this chapter, we will review functional brain imaging studies conducted in narcoleptic patients and evaluating different pathophysiological aspects of the disorder : (1) neurotransmission studies targeting the cholinergic, serotonergic, and dopaminergic systems (PET/SPECT); (2) the distribution of brain activity across the sleep-wake cycle (PET/SPECT); (3) the neural circuits involved in emotional and reward processing (fMRI).