In 19th-century psychiatry, monomania (from Greek monos, "one", and mania, meaning "madness" or "frenzy") was a form of partial insanity conceived as single psychological obsession in an otherwise sound mind.

[2]: 155 [3]: 26 Monomania may refer to: Partial insanity, variations of which enjoyed a long prehistory in jurisprudence, was in contrast to the traditional notion of total insanity, exemplified in the diagnosis of mania, as a global condition affecting all aspects of understanding and which reflected the position that the mind or soul was an indivisible entity.

[3]: 25–6, 31, 39 [6]: 243  Coined by the French psychiatrist Jean-Étienne Dominique Esquirol (1772–1840) around 1810,[2]: 153  monomania was a new disease-concept characterised by the presence of an expansive fixed idea, in which the mind was diseased and deranged in some facets but otherwise normal.

[2]: 157  Esquirol and his circle described three broad categories of monomania, consistent with their three-part classification of the mind into intellectual, emotional and volitional faculties.

[7]: 46  Emotional monomania is that in which the patient is obsessed with only one emotion or several related to it; intellectual monomania is that which is related to only one kind of delirious idea or ideas.