Cornelis Janssens van Ceulen (Dutch: [kɔrˈneːlɪs ˈjɑnsəns vɑn ˈkøːlən] or Cornelius Johnson; also Cornelius Jonson van Ceulen, Cornelis Jansz. van Ceulen and many other variants) (bapt. 14 October 1593 – bur. 5 August 1661) was an English painter of portraits of Dutch or Flemish parentage. He was active in England, from at least 1618 to 1643, when he moved to Middelburg in the Netherlands to escape the English Civil War. Between 1646 and 1652 he lived in Amsterdam, before settling in Utrecht, where he died.
Janssens painted many portraits of emerging new English gentry. His early portraits were panel paintings with "fictive" oval frames. His style varied considerably over his career, and he was able to assimilate new influences into his own style without any discordant effect. He was particularly accurate and detailed in his depiction of clothing.