Catherine Jagiellon (; ; 1 November 1526 – 16 September 1583) was a Polish princess and the wife of John III of Sweden. As such, she was Duchess of Finland (1562–83), Queen of Sweden (1569–83) and Grand Princess of Finland (1581–83). Catherine had significant influence over state affairs during the reign of her husband, and negotiated with the pope to introduce a counter reformation in Sweden.