Learner Tien (born December 2, 2005, in Irvine, California) is an American professional tennis player who has reached a career-high ATP singles ranking of world No. 12 (August 2026) and currently stands as the No. 3 American player. His standout professional achievements include winning two ATP Tour titles, the 2025 Next Gen ATP Finals, and reaching the quarterfinals of the 2026 Australian Open, his best major result. As the son of Vietnamese refugees, Tien picked up a racket at age 5 and won his first tournament immediately, later dominating the junior circuit with a 2023 Australian Open doubles title and finals appearances in the singles at both the 2023 Australian and US Opens. His breakthrough came in 2022 when he won the USTA Boys 18s National Championship, earning a wildcard into the 2022 US Open—making him the youngest male main-draw competitor there since 2005. In 2024, he captured Challenger titles in Cranbrook and Las Vegas, recorded his first ATP Tour wins, and rocketed into the top 130 by October 2024.