Cornelis Janssens van Ceulen (Dutch: [kɔrˈneːlɪs ˈjɑnsəns vɑn ˈkøːlən]; also Cornelius Jonson van Ceulen, Cornelius Johnson, 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, at least from 1618 to 1643. He moved to Middelburg in the Netherlands in 1643. Between 1646 and 1652 he lived in Amsterdam, before settling in Utrecht, where he was buried.
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 depiction of clothing.