Gilles Müller (born May 9, 1983) is a Luxembourgish professional tennis player. He was a US Open junior champion and is the most successful male tennis player in the history of his country. He was born, raised and currently resides in Schifflange.
In 2001, the year Müller turned pro, he reached the final of the boys' singles at the 2001 Wimbledon Championships, but was defeated by Swiss Roman Valent, 3–6, 7–5, 6–3. Later that year, Müller won the boys' singles final at the 2001 US Open by defeating Taiwanese Yeu-Tzuoo Wang, 7–6, 6–2. Müller finished the year 2001 as the world's no. 1 junior.
Remarkable results against top players were Müller's victories over Andy Roddick in the first round of the 2005 US Open, over Rafael Nadal at the 2005 Wimbledon Championships, and over Andre Agassi at the semifinals of the 2004 Legg Mason Tennis Classic in Washington, D.C..