BackgroundPsychiatry may face an “identity crisis” regarding its very foundations. The lack of consensus regarding the theoretical grounds of psychiatry as a discipline has its epicenter in the discussion about the Diagnostic and Statistical Manual (DSM). A growing number of academics considers the manual broken and a growing number of patients voice concern. Despite the huge body of critique, 90% of Randomized Trials are based on DSM definitions of mental disorder. Therefore, the question regarding the ontology of mental disorder remains: what is a mental disorder, exactly?AimsWe aim to identify ontologies that live among patients and clinicians, evaluate the degree of consistency and coherence between clinician and patient views and contribute to the establishment of a novel ontological paradigm of mental disorder that is aligned with patients’ and clinicians’ perspectives.MethodEighty participants (clinicians/patients/clinicians with lived experience) were interviewed using a semi-structured interview, exploring their ideas on the ontology of mental disorder. This question was approached from different angles which led to comprising the interview schedule into different topics: “concept of disorder,” “representation by DSM,” “what is treated,” “what is recovered,” and “the right outcome measure.” Interviews were transcribed and analyzed using inductive Thematic Analysis.ResultsFrom all subthemes and main themes, a typology was constructed in which six, not necessarily mutually exclusive, ontological domains were identified: mental disorder as (1) disease, (2) functional impairment, (3) loss of adaptation, (4) existential problem, (5) highly subjective phenomenon, and (6) deviation from social norms. Common ground for the sample groups was that mental disorder is about functional impairment. Although about a fourth of sample clinicians holds an ontological concept of disease, only a small percentage of patients and none of the clinicians with lived experience adhered to an ontological concept of disease. The sample clinicians most often understand mental disorder to be a highly subjective phenomenon, and individuals with lived experience (patients and clinicians) most often understand mental (dis)order to be adaptational in nature: an (im)balance of burden in relation to strengths, skills, and recourses.ConclusionThe ontological palette is more diverse than what is taught about mental disorder in dominant scientific and educational discourse. There is a need to diversify the current, dominant ontology and make room for other ontologies. Investment is required in the development, elaboration and coming of age of these alternative ontologies, allowing them to reach their full potential and act as drivers of a landscape of promising novel scientific and clinical approaches.