Robert Musil (Austrian German: [ˈroːbɛrt ˈmuːzɪl]; 6 November 1880 – 15 April 1942) was an Austrian philosophical writer. His unfinished novel, The Man Without Qualities (German: Der Mann ohne Eigenschaften), is generally considered to be one of the most important and influential modernist novels.

Musil was born in Klagenfurt, Carinthia, the son of engineer Alfred Edler Musil (1846, Temeswar/Timișoara – 1924) and his wife Hermine Bergauer (1853, Linz – 1924). The orientalist Alois Musil ("The Czech Lawrence") was his second cousin.

Soon after his birth, the family moved to Komotau/Chomutov in Bohemia, and in 1891 Musil's father was appointed to the chair of Mechanical Engineering at the German Technical University in Brünn/Brno and, later, he was raised to hereditary nobility in the Austro-Hungarian Empire. He was baptized Robert Mathias Musil and his name was officially Robert Mathias Edler von Musil from 22 October 1917, when his father was ennobled (made Edler), until 3 April 1919, when the use of noble titles was forbidden in Austria.

Musil was short in stature, but strong and skilled at wrestling, and by his early teens, he proved to be more than his parents could handle. They sent him to a military boarding school at Eisenstadt (1892–1894) and then Hranice (1894–1897). The school experiences are reflected in his first novel Die Verwirrungen des Zöglings Törless (The Confusions of Young Törless).

After graduation Musil studied at a military academy in Vienna during the fall of 1897, but then switched to mechanical engineering, joining his father's department at the Brno University of Technology. During his university studies, he studied engineering by day, and at night, read literature and philosophy and went to the theatre and art exhibitions. Friedrich Nietzsche, Fyodor Dostoyevsky, Ralph Waldo Emerson, and Ernst Mach were particular interests of his university years. Musil finished his studies in three years and, in 1902–1903, served as an unpaid assistant to Professor of Mechanical Engineering Carl von Bach [de], in Stuttgart. During that time, he began work on Young Törless.

He also invented Musilscher Farbkreisel [de], the Musil color top, a motorised device for producing mixed colours by additive colour-mixing with two differently colored, sectored, rotating discs. This was an improvement over earlier models, allowing a user to vary the proportions of the two colors during rotation and to read off those proportions precisely.

Musil's sexual life around the turn of the century, according to his own records, was mainly with a prostitute, which he treated partly as an experimental self-experience. But he also was infatuated with the pianist and mountaineer Valerie Hilpert, who assumed mystical features. In March 1902, Musil underwent treatment for syphilis with mercury ointment. During this time, his several years of relationship began with Hermine Dietz, the 'Tonka' of his own novel, published in 1923. Hermine's syphilitic miscarriage in 1906 and her death in 1907 may have been due to infection from Musil.

Musil grew tired of engineering and what he perceived as the limited world-view of the engineer. He launched himself into a new round of doctoral studies (1903–1908) in psychology and philosophy at the University of Berlin under Professor Carl Stumpf. In 1905, Musil met his future wife, Martha Marcovaldi (née Heimann, 21 January 1874 – 6 November 1949). She had been widowed and remarried, with two children, and was seven years older than Musil. His first novel, Young Törless, was published in 1906.