United States Anti-Doping Agency v. Lance Armstrong, the Lance Armstrong doping case, was a major doping investigation that led to retired American road racing cyclist Lance Armstrong being stripped of his seven consecutive Tour de France titles, along with one Olympic medal, and his eventual admission to using performance-enhancing drugs. The United States Anti-Doping Agency (USADA) portrayed Armstrong as the ringleader of what it called "the most sophisticated, professionalized and successful doping program that sport has ever seen."

For much of his career, Lance Armstrong faced persistent allegations of doping, but until 2006, no official investigation was undertaken. The first break in the case came in 2005 when SCA Promotions, a Dallas-based insurer, balked at paying a US$5 million bonus to Armstrong for winning his sixth consecutive Tour de France. SCA president Bob Hamman had read L.A. Confidentiel, a book by cycling journalists Pierre Ballester and David Walsh, which detailed circumstantial evidence of massive doping by Armstrong and members of his U.S. Postal Service Pro Cycling Team. In 2006, an arbitration panel ruled that SCA had to pay the bonus. However, Hamman's real goal was to force an investigation by sporting authorities, believing that if someone in a position to investigate the matter found that Armstrong had indeed doped, he could be stripped of his Tour victories – allowing SCA to get its money back. His hunch proved correct; officials from the United States Anti-Doping Agency (USADA) asked to review the evidence Hamman had gleaned.

U.S. federal prosecutors pursued allegations of doping by Armstrong from 2010 to 2012. The effort convened a grand jury to investigate doping charges, including taking statements under oath from Armstrong's former team members and other associates. They met with officials from France, Belgium, Spain, and Italy, and requested samples from the French anti-doping agency. The investigation was led by federal agent Jeff Novitzky, who also investigated suspicions of steroid use by baseball players Barry Bonds and Roger Clemens.

Armstrong's former teammate Floyd Landis was a key witness in the criminal investigation, and according to the book Wheelmen, Landis at one point wore a recording device and used a video camera disguised as a keychain, at the investigators' request in an attempt to gather evidence against a team owner in California. However, based on testimony from Landis, the prosecutors soon turned their attention to Armstrong and the doping that took place on the U.S. Postal Service team years earlier. As part of his campaign to clear his name from allegations of doping, Armstrong hired a Washington lobbying firm in 2010 to raise concerns about Novitzky, according to a story in The Wall Street Journal. The firm worked for Armstrong for about three months, but, after arranging meetings on Capitol Hill, decided a full-scale lobbying effort would not have worked.

On February 2, 2012, federal prosecutors officially dropped their criminal investigation with no charges. The closing of the case by U.S. Attorney André Birotte Jr. was not without controversy, with the decision coming as a surprise to many. In October 2012, Velonews announced they had filed a Freedom of Information Act request regarding the two-year Armstrong investigation and its dismissal.

In June 2012, USADA accused Armstrong of doping and drug trafficking, based on blood samples from 2009 and 2010, and testimonies from witnesses including former teammates. Armstrong, denying all doping use in a statement, was suspended from competition in cycling and triathlon. He was charged in a letter from USADA, along with five others, including former team manager Johan Bruyneel. USADA said Armstrong used banned substances, including the blood-booster erythropoietin (EPO) and steroids, as well as blood transfusions dating back to 1996.

In July 2012, Armstrong filed a lawsuit in the United States District Court for the Western District of Texas, requesting that the court "bar USADA from pursuing its case or issuing any sanctions against him" based on the claim that "USADA rules violate athletes' constitutional rights to a fair trial, and that the agency does not have jurisdiction in his case." On July 10, 2012, after U.S. District Judge Sam Sparks threw out the initial lawsuit for being overly lengthy, Armstrong filed a revised lawsuit. The same day, three of Armstrong's former associates from the U.S. Postal Service team—Luis Garcia del Moral, a team doctor; Michele Ferrari, a consulting doctor; and Jose "Pepe" Marti, team trainer—refused to take part in arbitration and were automatically banned from Olympic-level sports for life.

Judge Sparks ruled in favor of USADA on August 20, 2012, but questioned the timing and motivation of the agency's investigation of Armstrong, and their apparent "single minded determination to force Armstrong to arbitrate ... in direct conflict with [cycling governing body] UCI's equally evident desire not to proceed against him." Applying rational basis review to the Federal Arbitration Act, the Stevens Amateur Sports Act, and various governing documents of USADA, U.S. Cycling and the U.S. Olympic Committee, Sparks upheld USADA's authority to investigate Armstrong and initiate arbitration against him, and that Armstrong's right to due process could not be violated by USADA before any proceedings had actually occurred.