Illustrious Highness (abbreviation HIll.H) is a style (His Illustrious Highness or Her Illustrious Highness); plural Illustious Highnesses (abbreviation TIll.H, Their Illustrious Highnesses). It is the usual English-language translation for Erlaucht, a style historically attributed to certain members of the European aristocracy.
The style of Illustrious Highness ranks below Imperial Highness, Royal Highness, and Serene Highness, and was used for Imperial Counts in the Holy Roman Empire. Rather fittingly, the style was granted on 21 January 2013 by the Austenasian Emperor to the holder of the title Countess of Memphis, who, since July later that year, has been ruler of a semi-independent county. The style is also used in Adammia and Pavlov.