Solomon Naumovich Rabinovich, better known under his pen name Sholem Aleichem, was a Yiddish author and playwright who lived in the Russian Empire and in the United States. The 1964 musical Fiddler on the Roof, based on Aleichem's stories about Tevye the Dairyman, was the first commercially successful English-language stage production about Jewish life in Eastern Europe.

Sidney Clopton Lanier was an American musician, poet and author. He served in the Confederate States Army as a private, worked on a blockade-running ship for which he was imprisoned, taught, worked at a hotel where he gave musical performances, was a church organist, and worked as a lawyer. As a poet he sometimes used dialects. Many of his poems are written in heightened, but often archaic, American English. He became a flautist and sold poems to publications. He eventually became a professor of literature at the Johns Hopkins University in Baltimore, and is known for his adaptation of musical meter to poetry. Many schools, other structures and two lakes are named for him, and he became hailed in the South as the "poet of the Confederacy". A 1972 US postage stamp honored him as an "American poet".

Sidney Royse Lysaght was a British writer of Irish ancestry.

Sidonie Matsner Gruenberg (1881–1974) was a parenting expert, writer, and director of the Child Study Association of America.

Siegfried Loraine Sassoon was an English war poet, writer, and soldier. Decorated for bravery on the Western Front, he became one of the leading poets of the First World War. His poetry both described the horrors of the trenches and satirized the patriotic pretensions of those who, in Sassoon's view, were responsible for a jingoism-fuelled war. Sassoon became a focal point for dissent within the armed forces when he made a lone protest against the continuation of the war with his "Soldier's Declaration" of July 1917, which resulted in his being sent to the Craiglockhart War Hospital. During this period he met and formed a friendship with Wilfred Owen, who was greatly influenced by him. Sassoon later won acclaim for his prose work, notably his three-volume, fictionalised autobiography, collectively known as the Sherston trilogy.

Sigfrid Siwertz was a Swedish novelist and poet. He was born and died in Stockholm.

Sigmund Freud was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating pathologies seen as originating from conflicts in the psyche, through dialogue between patient and psychoanalyst, and the distinctive theory of mind and human agency derived from it.

Sigrid Undset was a Danish-born Norwegian novelist. She was awarded the Nobel Prize for Literature in 1928.

Silvanus Phillips Thompson was an English professor of physics at the City and Guilds Technical College in Finsbury, England. He was elected to the Royal Society in 1891 and was known for his work as an electrical engineer and as an author. Thompson's most enduring publication is his 1910 text Calculus Made Easy, which teaches the fundamentals of infinitesimal calculus, and is still in print. Thompson also wrote a popular physics text, Elementary Lessons in Electricity and Magnetism, as well as biographies of Lord Kelvin and Michael Faraday.

Silvio Pellico was an Italian writer, poet, dramatist and patriot active in the Italian unification.