Functional neurological disorder (FND), also known as functional neurological symptom disorder (conversion disorder) in the DSM-5-TR (APA, Diagnostic and statistical manual of mental disorders. American Psychiatric Association, 2022) and dissociative neurological symptom disorder in the ICD-11 (WHO, International statistical classification of diseases and related health problems. WHO, 2019), refers to a highly heterogenous category of conditions characterized by one or more symptoms of involuntary alteration in motor, sensory, or cognitive functioning that are incompatible with recognized neurological or other medical conditions. FND is highly prevalent, leads to significant healthcare expenditures, and may result in disability, yet despite its ubiquity, FND has proved to be challenging to understand, diagnose, and effectively treat. So much so that FND has been referred to as a “silent epidemic” in medicine and a “blind spot” or “crisis” for psychiatry and neurology (see Aybek and Perez, BMJ 376:o64, 2022). Fortunately, researchers have made significant advances in terms of understanding the pathophysiology of FND, as well as in diagnosis and treatment. FND is now increasingly considered a disorder emerging from neural network dysfunction, most likely including alterations within brain circuits involved in emotion processing, agency, attention, interoception, and predictive processing (Aybek and Perez, BMJ 376:o64, 2022; Drane et al., CNS Spectrums 26:555–561, 2021). After briefly reviewing the history of FND, this chapter provides an overview of current diagnostic criteria, contemporary etiological theory, and epidemiology of FND, as well as discussing considerations for FND within the neuropsychology clinic.