Esther Szekeres (born Klein) (20 February 1910 – 28 August 2005) was a Hungarian-Australian mathematician. Esther Szekeres's Erdős number is 1.
As a young woman in Budapest she was part of a group that included Paul Erdős, George Szekeres and Paul Turán, who met over interesting mathematical problems. In 1933, Esther proposed a combinatorial problem to the group that came to be named by Erdős as the Happy Ending problem, because it led to her marriage with George Szekeres in 1937.
Following the outbreak of World War II, Esther and George Szekeres emigrated to Australia after spending several years in Hongkew (a community of refugees) located in Shanghai, China. In Australia they originally settled in Adelaide, before moving to Sydney in the 1960s.
In Sydney, Esther lectured at Macquarie University and was actively involved in mathematics enrichment for high school students. In 1984, she jointly founded a weekly mathematics enrichment meeting that has since expanded into a program of about 30 groups that continue to meet weekly and inspire high school students throughout Australia and New Zealand.
In 2004, she and George moved back to Adelaide, where, on 28 August 2005, she and her husband died within an hour of each other.