Samantha Jane Stosur ( STOH-sər; born 30 March 1984) is an Australian professional tennis player. She is a former world No. 1 in doubles, a ranking which she held for 61 weeks, and a former world No. 4 in singles. Additionally, Stosur was the top-ranked Australian singles player for 452 consecutive weeks, from October 2008 to June 2017.

Stosur won the 2011 US Open, defeating Serena Williams in the final and becoming the first Australian woman since Evonne Goolagong Cawley in 1980 to win a Grand Slam singles tournament. Stosur has won five other Grand Slam titles to date: the 2005 US Open and 2006 French Open women's doubles events, and the 2005 Australian Open, 2008 Wimbledon Championships and 2014 Wimbledon Championships mixed doubles events.

In addition, she finished runner-up at six other Grand Slam events, including the singles at the 2010 French Open, where she defeated four-time champion Justine Henin, ending her 24-match winning streak at the tournament, and world No. 1 Serena Williams en route to the final. She also reached three additional semifinals at the French Open in 2009, 2012, and 2016.