Mary Somerville (née Fairfax, formerly Greig; 1780–1872) was a Scottish scientist, writer, and polymath. She studied mathematics and astronomy, and in 1835 she and Caroline Herschel were elected as the first female Honorary Members of the Royal Astronomical Society.

In John Stuart Mill's 1866 mass petition to the UK Parliament to grant women the right to vote, the first signature on the petition was Somerville's, which she signed before the age of 86.

When she died in 1872, The Morning Post declared in her obituary that "Whatever difficulty we might experience in the middle of the nineteenth century in choosing a king of science, there could be no question whatever as to the queen of science". The first use of the word "scientist" in the English language was in a review by William Whewell of Somerville's second book On the Connexion of the Physical Sciences. Beyond her work as a scientist, she is known and celebrated as a mathematician and philosopher.

Somerville College, a college of the University of Oxford, is named after her, reflecting the virtues of liberalism and academic success that the college wished to embody. She is featured on the front of the Royal Bank of Scotland polymer £10 note launched in 2017 along with a quotation from On the Connexion of the Physical Sciences.

Somerville, the daughter of Vice-Admiral Sir William George Fairfax, was related to several prominent Scottish houses through her mother, Margaret Charters. She was born on 26 December 1780 at the manse of Jedburgh, the home of her maternal aunt and the Rev. Dr. Thomas Somerville (1741–1830) (author of My Own Life and Times). Her childhood home was at Burntisland, Fife, where her mother was from.

Somerville was the second of four surviving children (three of her siblings had died in infancy). She was particularly close to her oldest brother Sam. The family lived in genteel poverty as her father's naval pay remained meagre, despite his rise through the ranks. Her mother supplemented the household's income by growing vegetables, maintaining an orchard and keeping cows for milk. Her mother taught her to read the Bible and Calvinist catechisms. When her household chores were done, Mary was free to roam among the birds and flowers in the garden.

In her autobiography, Somerville recollects that on her father's return from sea he said to his wife, "This kind of life will never do, Mary must at least know how to write and keep accounts". Ten-year-old Mary was then sent to an expensive boarding school in Musselburgh, where she learned the first principles of writing, rudimentary French and English grammar. Upon returning home, she:

...was no longer amused in the gardens, but wandered about the country. When the tide was out I spent hours on the sands, looking at the star-fish and sea-urchins, or watching the children digging for sand-eels, cockles, and the spouting razor-fish. I made collections of shells, such as were cast ashore, some so small that they appeared like white specks in patches of black sand. There was a small pier on the sands for shipping limestone brought from the coal mines inland. I was astonished to see the surface of these blocks of stone covered with beautiful impressions of what seemed to be leaves; how they got there I could not imagine, but I picked up the broken bits, and even large pieces, and brought them to my repository.