The Booker Prize has been awarded jointly to two authors three times: in 1974, 1992 and 2019.
The first shared award came in 1974, when Nadine Gordimer won for The Conservationist and Stanley Middleton won for Holiday. The prize was shared again in 1992 by Barry Unsworth, for Sacred Hunger, and Michael Ondaatje, for The English Patient.
The third joint award occurred in 2019, when Margaret Atwood won for The Testaments and Bernardine Evaristo won for Girl, Woman, Other. This decision was especially notable because the rules had been changed after 1992 to discourage joint winners, but the judging panel refused to separate the two books.
A common mix-up is to confuse jointly awarded prizes with years in which several books reached the shortlist. Only the three years above involved two books being officially declared Booker Prize winners.