Nicolas Kiefer (born 5 July 1977), is a former German professional tennis player. He reached the semifinal of the 2006 Australian Open and won a Silver medal in Men's Doubles with partner Rainer Schüttler at the 2004 Summer Olympics in Athens. Kiefer's career-high singles ranking was World No. 4, achieved in January 2000.
Kiefer was taken notice of as an outstanding junior. He won the Junior Australian Open, US Open and was a finalist and semi-finalist at Wimbledon and the French Open finishing as the No. 2 junior behind Mariano Zabaleta when he was 18 in 1995.
On 10 January 2000, he reached his second quarter-final at the Australian Open and afterwards was ranked World No. 4, his highest position to date.
Nicolas has been known to have a few tennis superstitions. He is sometimes seen tapping his racquet on the corners of the court after a point, although the reasons behind this are not clear. He also, when serving, frequently asks for the ball with which he has just won a point to re-use it in the next one.