Catherine Jagiellon (Polish: Katarzyna Jagiellonka; Swedish: Katarina Jagellonica, Lithuanian: Kotryna Jogailate; 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 spouse, and negotiated with the pope to introduce a counter reformation in Sweden.
She was the mother of the future Sigismund III Vasa, King of Poland.