The Great Barrington Declaration is an open letter published in October 2020 in response to the COVID-19 pandemic and lockdowns. It claimed that COVID-19 lockdowns could be avoided via the fringe notion of "focused protection", by which those most at risk of dying from an infection could purportedly be kept safe while society otherwise took no steps to prevent infection. The envisaged result was herd immunity as SARS-CoV-2 swept through the population.

Signed by Sunetra Gupta of the University of Oxford, Jay Bhattacharya of Stanford University, and Martin Kulldorff of Harvard University, it was sponsored by the American Institute for Economic Research (AIER), a libertarian free-market think tank associated with climate change denial. The declaration was drafted in Great Barrington, Massachusetts, signed there on 4 October 2020, and published on 5 October. At the time, COVID-19 vaccines were considered to be months away from general availability. The document presumed that the disease burden of mass infection could be tolerated, that any infection would confer long term sterilizing immunity, and it made no mention of physical distancing, masks, contact tracing, or long COVID, which has left patients with debilitating symptoms months after the initial infection.

The World Health Organization (WHO) and numerous academic and public-health bodies stated that the strategy would be dangerous and lacked a sound scientific basis. They said that it would be challenging to shield all those who are medically vulnerable, leading to a large number of avoidable deaths among both older people and younger people with pre-existing health conditions, and warned that the long-term effects of COVID-19 were still not fully understood. Moreover, the WHO said that the herd immunity component of the proposed strategy is undermined by the unknown duration of post-infection immunity. They said that the more likely outcome would be recurrent epidemics, as was the case with numerous infectious diseases before the advent of vaccination. The American Public Health Association and 13 other public-health groups in the United States warned in a joint open letter that the "Great Barrington Declaration is not grounded in science and is dangerous". The Great Barrington Declaration received support from the Donald Trump administration, British Conservative politicians, and from The Wall Street Journal's editorial board.