Sir Edmund Taylor Whittaker (24 October 1873 – 24 March 1956) was a British mathematician, physicist, and historian of science. Whittaker was a leading mathematical scholar of the early 20th century who contributed widely to applied mathematics and was renowned for his research in mathematical physics and numerical analysis, including the theory of special functions, along with his contributions to astronomy, celestial mechanics, the history of physics, and digital signal processing.

Among the most influential publications in Whittaker's bibliography, he authored several popular reference works in mathematics, physics, and the history of science, including A Course of Modern Analysis (better known as Whittaker and Watson), Analytical Dynamics of Particles and Rigid Bodies, and A History of the Theories of Aether and Electricity. Whittaker is also remembered for his role in the relativity priority dispute, as he credited Henri Poincaré and Hendrik Lorentz with developing special relativity in the second volume of his History, a dispute which has lasted several decades, though scientific consensus has remained with Einstein.

Whittaker served as the Royal Astronomer of Ireland early in his career, a position he held from 1906 through 1912, before moving on to the chair of mathematics at the University of Edinburgh for the next three decades and, towards the end of his career, received the Copley Medal and was knighted. The School of Mathematics of the University of Edinburgh holds The Whittaker Colloquium, a yearly lecture, in his honour and the Edinburgh Mathematical Society promotes an outstanding young Scottish mathematician once every four years with the Sir Edmund Whittaker Memorial Prize, also given in his honour.

Edmund Taylor Whittaker was born in Southport, in Lancashire, the son of Selina Septima (née Taylor) and John Whittaker. He was described as an "extremely delicate child", necessitating his mother to home school him until he was 11 years old, when he was sent off to Manchester Grammar School. Ernest Barker, a classmate of Whittaker's at the Grammar School with whom he shared the office of prefect, later recalled his personality: "He had a gay, lively, bubbling spirit: he was ready for every prank: he survives in my memory as a natural actor; and I think he could also, on occasion, produce a merry poem." While at the school, Whittaker studied on the "classical side", devoting three-fifths of his time to Latin and Greek. Whittaker struggled with the poetry and drama which was required by the upper school, and expressed gratitude for being allowed to leave these studies behind and specialise in mathematics.

In December 1891 Whittaker received an entrance scholarship to Trinity College, Cambridge. After completing his education at the Manchester Grammar School he went on to study mathematics and physics there from 1892 to 1895. He entered Trinity College as a minor scholar in October 1892 to study mathematics. Whittaker was the pupil of Andrew Russell Forsyth and George Howard Darwin while at Trinity College and received tutoring throughout his first two years. With an interest more in applied than pure mathematics, Whittaker won the Sheepshanks Astronomical Exhibition in 1894 as an undergraduate. He graduated as Second Wrangler in the Cambridge Tripos examination in 1895. The Senior Wrangler that year was Thomas John I'Anson Bromwich and Whittaker tied John Hilton Grace for second, all three along with three other participants, including Bertram Hopkinson, went on to be elected Fellows of the Royal Society. He also received the Tyson Medal for Mathematics and Astronomy in 1896.

Whittaker was a fellow of Trinity College, Cambridge from 1896 to 1906 when he was appointed Andrews Professor of Astronomy at Trinity College Dublin and Royal Astronomer of Ireland. He held these posts until 1912, when he was appointed chair of mathematics at the University of Edinburgh, a role he went on to hold for just over a third of a century. Throughout his career, he wrote papers on automorphic functions and special functions in pure mathematics as well as on electromagnetism, general relativity, numerical analysis and astronomy in applied mathematics and physics, and was also interested in topics in biography, history, philosophy and theology. He also made several important innovations in Edinburgh that had a large impact on mathematical education and societies there.

In 1896, Whittaker was elected as a Fellow of Trinity College, Cambridge, and remained at Cambridge as a teacher until 1906. In 1897, Whittaker was awarded the Smith Prize for his work on the paper "On the connexion of algebraic functions with automorphic functions", published in 1888.

In 1902, Whittaker found a general solution to Laplace's equation, which received popular news coverage as a "remarkable discovery", though the mathematician Horace Lamb noted that it did not offer any new features. He also wrote several celebrated books in his early career, publishing A Course of Modern Analysis in 1902 and following it up with A Treatise on the Analytical Dynamics of Particles and Rigid Bodies just two years later in 1904. In September of that year, Whittaker was forced to sell six silver forks at an auction to pay back taxes which he had previously refused to pay due to the Education Act 1902 requiring citizens to pay taxes to fund local Christian schools, such as the Roman Catholic Church and the Church of England.