Mary Berenson (Pennsylvania, 1864 – 1945), née Mary Smith, was an art historian, now thought to have had a large hand in some of the writings of her second husband, Bernard Berenson.
Her father was Robert Pearsall Smith, her mother Hannah Whitall Smith. She studied at the Harvard Annex in 1884-1885. Here Mary met the Irish barrister Benjamin Conn "Frank" Costelloe, who she married in 1885. This marriage was the occasion for the whole family, including her brother Logan Pearsall Smith and sister Alys Pearsall Smith to move to England in 1888. Mary separated from Costelloe, with whom she had two children, after a few years together. She took up in Italy with Bernard Berenson, whom she eventually married in 1900.
Subsequently she brought together a social circle at Villa I Tatti', the Berenson home, and developed its gardens.