Anthony Stephen Fauci ForMemRS (/ˈfaʊtʃi/ FOW-chee; born December 24, 1940) is an American physician-scientist and immunologist who served as the director of the National Institute of Allergy and Infectious Diseases (NIAID) from 1984 to 2022, and the chief medical advisor to the president from 2021 to 2022. Fauci was one of the world's most frequently cited scientists across all scientific journals from 1983 to 2002. In 2008, President George W. Bush awarded him the Presidential Medal of Freedom, the highest civilian award in the United States, for his work on the AIDS relief program PEPFAR.

Fauci received his undergraduate education at the College of the Holy Cross and his Doctor of Medicine from Cornell University. As a physician with the National Institutes of Health (NIH), Fauci served the American public health sector for more than fifty years and has acted as an advisor to every U.S. president since Ronald Reagan. During his time as director of the NIAID, he made contributions to HIV/AIDS research and other immunodeficiency diseases, both as a research scientist and as the head of the NIAID.

During the COVID-19 pandemic, Fauci served under President Donald Trump as one of the lead members of the White House Coronavirus Task Force. His advice was frequently contradicted by Trump, and Trump's supporters alleged that Fauci was trying to politically undermine Trump's run for reelection. During the Biden administration, Fauci served as one of the lead members of the White House COVID-19 Response Team and as Biden's chief medical advisor.

Fauci was born on December 24, 1940, in Brooklyn, New York City, to Stephen A. (1910–2008) and Eugenia Lillian (née Abys; 1909–1965) Fauci as the youngest of two children. His father, a pharmacist, attended Columbia University and owned a drug store. Fauci worked with his mother and sister at the pharmacy's register and also delivered prescriptions. The pharmacy was located in the Dyker Heights section of Brooklyn, directly beneath the family apartment, previously in the Bensonhurst neighborhood. When he was a child, Fauci developed a fascination with World War II, and played basketball and baseball.

Fauci's grandparents immigrated to the United States from Italy in the late 19th century. His paternal grandparents, Antonino Fauci and Calogera Guardino, were from Sciacca, Sicily, and his maternal grandparents were from Naples. His maternal grandmother, Raffaella Trematerra, was a seamstress and his maternal grandfather, Giovanni Abys, was a Swiss-born artist noted for his landscape and portrait painting, magazine illustrations in Italy, as well as graphic design for commercial labels. Fauci grew up Catholic, but also considers himself a humanist who "has faith in the goodness of mankind", stating that he thinks "that there are a lot of things about organized religion that are unfortunate, and [that he tends] to like to stay away from it." In December 2023, Fauci stated that he still considers himself a Roman Catholic, but he does not practice his faith anymore for "a number of complicated reasons"; clarifying his relationship with the Catholic Church, he stated:

I'm not against it. I identify myself as a Catholic. I was raised, I was baptized, I was confirmed, I was married in the Church. My children were baptized in the Church. But as far as practicing it, it seems almost like a pro forma thing that I don't really need to do.

Fauci attended Regis High School, a competitive Jesuit school on Manhattan's Upper East Side, where he captained the school's basketball team despite standing only 5 ft 7 in (1.70 m) tall. He decided halfway through high school to become a physician. After graduating in 1958, Fauci enrolled in the College of the Holy Cross, where he studied classical Greek and worked in a construction gang during the summers. He graduated from Holy Cross in 1962 with a Bachelor of Arts degree in classics with a pre-med track. Fauci then attended Cornell University's Medical College (now Weill Cornell Medicine), graduating with a Doctor of Medicine degree in 1966 ranked first in his class. At Cornell, he focused on adult internal medicine, mainly infectious diseases and the immune system. Fauci then did an internship and residency in internal medicine at New York Hospital-Cornell Medical Center (now Weill Cornell Medical Center).

After completing his medical residency in 1968, Fauci joined the National Institutes of Health (NIH) as a clinical associate in the National Institute of Allergy and Infectious Diseases's (NIAID) Laboratory of Clinical Investigation (LCI). He became head of the LCI's Clinical Physiology Section in 1974, and in 1980 was appointed chief of the NIAID's Laboratory of Immunoregulation. He became director of the NIAID in 1984. Fauci has been offered the position of director of the NIH several times, but has declined each time.