Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unsafe sex, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth (perinatal transmission). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world.

Peter H. Duesberg (born December 2, 1936 in Münster, Germany) is a professor of molecular and cell biology at the University of California, Berkeley. He is known for his cancer research and for his central role in AIDS denialism as an early and vocal proponent of the belief that HIV does not cause AIDS.

Duesberg received acclaim early in his career for research on oncogenes and cancer. With Peter Vogt, he reported in 1970 that a cancer-causing virus of birds had extra genetic material compared with non-cancer-causing viruses, hypothesizing that this material contributed to cancer. At the age of 36, Duesberg was awarded tenure at the University of California, Berkeley, and at 49, he was elected to the National Academy of Sciences. He received an Outstanding Investigator Grant (OIG) from the National Institutes of Health (NIH) in 1986, and from 1986 to 1987 was a Fogarty Scholar-in-Residence at the NIH laboratories in Bethesda, Maryland.

Long considered a contrarian by his scientific colleagues, Duesberg began to gain public notoriety with a March 1987 article in Cancer Research entitled "Retroviruses as Carcinogens and Pathogens: Expectations and Reality". In this and subsequent writings, Duesberg proposed his hypothesis that AIDS is caused by long-term consumption of recreational drugs and/or antiretroviral drugs, and that HIV is a harmless passenger virus. The scientific consensus is that HIV is the causal pathogen that leads to AIDS; Duesberg's HIV/AIDS claims have been rejected as incorrect and disproven by the scientific community. Reviews of his opinions in Nature and Science asserted that they were unpersuasive and based on selective reading of the literature, and that although Duesberg had a right to a dissenting opinion, his failure to fairly review the evidence for HIV causing AIDS meant that his opinion lacked credibility.