A former midfielder, Klein spent the entirety of his 12-year professional career playing in Major League Soccer, for the Kansas City Wizards, Real Salt Lake and Los Angeles Galaxy, winning the MLS Cup and Supporters' Shield with Kansas City in 2000, and the Supporters' Shield with Los Angeles in 2010, his last year as a professional.

[1] Klein was also a veteran member of the United States national team during the early 2000s; he acquired 23 caps, scored 5 goals, and represented his country at the 2003 Confederations Cup.

Klein attended De Smet Jesuit High School, winning a Missouri state championship in the fall of 1993.

Klein has been an equally important part of the Wizards midfield for the last four years, although his 2004 campaign was cut short by a torn ACL.

[2] On June 21, 2007, Klein was traded to Los Angeles Galaxy for midfielder Nathan Sturgis and forward Robbie Findley.