Colleen "CoCo" Vandeweghe (/ˈvændəweɪ/ VAN-də-way) (born Colleen Mullarkey; December 6, 1991) is an American professional tennis player. A former Junior US Open champion and top 10 singles player, she has also won two WTA titles, both at the Rosmalen Grass Court Championships in Den Bosch. In 2017, she reached two Grand Slam semifinals and the final of the WTA Elite Trophy to move into the top 10 for the first time. She reached her career-high singles ranking of world No. 9 on January 15, 2018. In addition to her two Grand Slam semifinals in 2017 at the Australian Open and the US Open, Vandeweghe has twice reached the quarterfinals at Wimbledon in both 2015 and 2017. Vandeweghe also owns one Grand Slam doubles title, which she won at the 2018 US Open with partner Ashleigh Barty.