CoCo Vandeweghe ( VAN-də-way) (born Colleen Mullarkey; December 6, 1991) is an American former professional tennis player. A former junior US Open champion and top 10 singles player, she won two WTA Tour titles, both at the Rosmalen Grass Court Championships. In 2017, she reached two major semifinals and the final of the WTA Elite Trophy to enter the top 10, reaching her career-high singles ranking of world No. 9 in January 2018. In addition, Vandeweghe twice reached the quarterfinals at Wimbledon in both 2015 and 2017. Vandeweghe also won one major doubles title, which she won at the 2018 US Open with partner Ashleigh Barty.
Despite being predominantly a singles player, she also exceled at doubles. In 2016, she partnered with Martina Hingis in much of the second half of the season and reached the semifinals of the US Open, a performance that lifted her to a then-career-high ranking of No. 18 in the world. In 2018, Vandeweghe won her first Grand Slam title, partnering Ashleigh Barty at the US Open. Later on, they reached the semifinals at the 2018 WTA Finals, lifting Vandeweghe to a new career-high ranking of No. 14. She is also a two-time Grand Slam finalist in mixed doubles, reaching the final at the 2016 Australian Open with Horia Tecău and the 2016 US Open with compatriot Rajeev Ram.
Vandeweghe's prowess at both singles and doubles helped her win all eight of her Fed Cup rubbers in 2017 across three different ties to lead the U.S. team to its first championship since 2000. Her best surface was grass.