This chapter traces the historical and conceptual evolution of schizophrenia as a diagnostic category and examines its persistent complexity and contested status. This evolution is a product of overlapping clinical characterisations, shifting theoretical frameworks, and multiple research agendas. Two competing perspectives on its ontological status are entertained with the goal of finding a productive synthesis: the continuity hypothesis, which treats schizophrenia as a stable brain disorder recognisable across time, and the discontinuity thesis, which frames it as a culturally and historically situated construct without essential unity. Although the term ‘schizophrenia’ has endured for over a century, its referents have varied, and its boundaries remain diffuse. Clinical presentations are heterogeneous, outcomes are variable, and underlying mechanisms are diverse—ranging from neurodevelopmental disruptions to immune-mediated processes. These complexities challenge attempts to define schizophrenia as a natural kind or unitary disease entity. At the clinical level, it remains a disorder marked by persistent disturbances in selfhood, perception, cognition, affect, and social functioning. Contemporary advances in neuroscience, genetics, and immunology have refined our understanding of these disturbances, generating new explanatory models while also exposing the limitations of traditional nosologies. The recognition of autoimmune psychosis and other neurologically identifiable causes of schizophrenia-like syndromes illustrates that neuropsychiatric disorders remain relevant to schizophrenia. Schizophrenia is not a discrete disease entity; it is a historically contingent and evolving set of clinical concepts.