Jan Ingenhousz, Dutch physician, physiologist, and botanist (d. 1799)
Jan (or John) Ingenhousz or Ingen-Housz FRS (8 December 1730 – 7 September 1799) was a Dutch physiologist, biologist and chemist.

He is best known for discovering photosynthesis by showing that light is essential to the process by which green plants absorb carbon dioxide and release oxygen. He also discovered that plants, like animals, have cellular respiration. In his lifetime he was known for successfully inoculating the members of the Habsburg family in Vienna against smallpox in 1768 and subsequently being the private counsellor and personal physician to the Austrian Empress Maria Theresa.