The concept of mental disorder has many facets. Specific concepts of disease or disorder stand for individual entities, classified as diagnoses. Ideally, they are based on discrete physical, neurobiological or - as is the case with hereditary diseases - genetic findings. However, the majority of mental disorders are still lacking such biological bases of definition. Hence, mental disorders of unknown origin are classified by their patterns of symptoms that show an above-chance co-occurrence and run a similar course.Behind the specific concepts of disease and disorder lies a general concept. It plays a significant role in daily life and underlies the context-specific notions. It defines what constitutes being ill as such independently of diagnosis. In everyday life we frequently experience being ill without at first knowing what we are actually suffering from. Perceivable signs indicating mental disorder in general include pain, fever, physical weakness, irritability, depressiveness, disturbed sleep and cognitive and other types of dysfunction. Various conditions are characterized by a prodromal stage before a sufficient number of typical symptoms permitting a diagnosis appear.Typical of disease or disorder is its progression, a course over time leading to deterioration or improvement, to recovery or a fatal end. Syndromes that show no variation over time are no longer classified as mental disorders, but as personality disorders or disabilities (e. g. mental disability) - formerly infirmities - mostly cognitive in type. Contextual concepts of mental disorder encompass a general concept, used in day-to-day life, and the medical or specific concepts mainly define the individual disorders via diagnoses. The social and legal contexts of mental disorder will also be discussed.