The United States Anti-Doping Agency (USADA, yoo-SAH-duh) is a non-profit, non-governmental 501(c)(3) organization and the national anti-doping organization (NADO) for the United States. To protect clean competition and the integrity of sport and prevent doping in the United States with a performance-enhancing substance, the USADA provides education, leads scientific initiatives, conducts testing, and oversees the results management process. Headquartered in Colorado Springs, Colorado, USADA is a signatory to the World Anti-Doping Code, which harmonizes anti-doping practices around the world, and is widely considered the basis for the strongest and strictest anti-doping programs to prevent doping in sport.

In 2001, USADA was recognized by the U.S. Congress as "the official anti-doping agency for Olympic, Pan American and Paralympic sport in the United States." While USADA is not a government entity, it is partly funded by the Office of National Drug Control Policy (ONDCP), with its remaining budget generated from contracts for anti-doping services with sport organizations, most notably the United States Olympic and Paralympic Committee (USOPC). The United States has also ratified the UNESCO International Convention against Doping in Sport, the first global international treaty against doping in sport, and largely relies on USADA to carry out this commitment.

Travis Tygart has been the chief executive officer of USADA since September 2007.

In October 1999, the USOC launched USADA and operations began on October 1, 2000. In 2003, one of USADA's first major undertakings was the revision of the then-current United States anti-doping policies in order to bring them into compliance with the newly adopted World Anti-Doping Code. One of the major adjustments made to the Code by USADA included reducing the standard of proof required in doping-related adjudication. Before modifications, the standard of proof was equal to that required in a United States court of law. After modification, USADA reduced the standard required to establish a doping violation to "comfortable satisfaction of a hearing body".

Notably, USADA were contracted by the UFC to act as an anti-doping authority within the organization, with the partnership beginning in 2015. However, during a publicized dispute over the eligibility of Conor McGregor to rejoin the UFC's roster following a period of absence from USADA's athlete testing pool, USADA announced that they would not renew their contract with the UFC. The deal between USADA and the UFC is set to expire in 2024, after which the UFC's roster will no longer be subject to USADA testing.

Currently, USADA's status and independence from the USOPC contrasts the norm in sport in the United States, as most professional sport organizations (MLB, NFL, NBA, NHL) manage the anti-doping functions of their own sports. As a result of USADA's ongoing multi-year contracts with the USOPC and the sport national governing bodies (USA Track & Field, USA Cycling, USA Swimming, US Soccer, etc.), the agency is responsible for managing anti-doping programs, including testing and results management, for each sport's athletes and events throughout the year. Despite its name and status as the country's official anti-doping organization, USADA is a private organization and not subject to government oversight.^{[citation needed]}

USADA is responsible for implementation of the World Anti-Doping Agency's Code (Code) in the United States. The Code is the core document that harmonizes anti-doping policies, rules, and regulations within sport organizations and among public authorities around the world. It works in conjunction with five International Standards, which aim to foster consistency among anti-doping organizations in: testing; laboratories; therapeutic use exemptions; the list of prohibited substances and methods; and the protection of privacy and personal information. The Code's International Standards are as follows:

The International Olympic Committee (IOC) required that all Olympic sports adopt the World Anti-Doping Code prior to August 13, 2004.