After nearly a century of intensive research and clinical investigation, the pathophysiology of psychiatric disorders remains an enigma. Short of a clear understanding of how psychiatric symptoms are produced, the various cognitive, emotional, and behavior patterns that characterize psychiatric disorders continue to be grouped into syndromes and treated accordingly. The weakness of this approach is that the treatment is administered without a clear understanding of what pathological process is being treated. Moreover, the symptoms of most psychiatric disorders are frequently changing and melding into one another. This leads to diagnostic confusion, medication stacking, and poor treatment outcomes, all of which erode patient trust and perpetuate the stigma of mental illness. In this seminal report, a new hypothesis on the pathophysiology of psychiatric disorders will be presented based on multidisciplinary evidence that nearly all psychiatric disorders and their functional comorbidities are rooted in a single, shared, neurophysiological abnormality. The report will then trace that abnormality to its molecular roots and introduce a new paradigm through which the many faces of mental illness can be understood and uniformly treated. The Multi-Circuit Neuronal Hyperexcitability hypothesis of psychiatric disorders posits that an inherent hyperexcitability of the neurological system is at the root of mental illness and provides a precise, functionallyspecific framework that eliminates diagnostic confusion, informs a unified treatment approach, and helps remove the long-held stigma of mental illness. + Itemized comparison showing that the same conditions and chemicals that increase the potential for seizures (upper section) also increase the potential for psychiatric symptoms, and the same conditions and chemicals that decrease the potential for seizures (lower section) also decrease the potential for psychiatric symptoms.