Logan Pearsall Smith (18 October 1865 – 2 March 1946) was an American-born essayist and critic.
Smith was born in Millville, New Jersey the son of the prominent Quakers Robert Pearsall Smith and Hannah Whitall Smith. His father's family had become wealthy from its glass factories. He lived for a time as a boy in England, and later attended Haverford College and Harvard College; in his 1938 autobiography he describes how in his youth he came to be a friend of Walt Whitman in the poet's latter years. Smith later studied at Balliol College, Oxford, where he graduated in 1891. He then settled in England with occasional forays to continental Europe and became a British citizen in 1913. He divided his time between Chelsea, where he was a close friend of Desmond MacCarthy, and a Tudor farmhouse near the Solent, called "Big Chilling". Smith employed a succession of young secretary/companions to help him. This post was Cyril Connolly's first job in 1925 and he was to be strongly influenced by Smith. Robert Gathorne-Hardy succeeded Connolly in this post.
Smith was an authority on 17th century divines. He was known for his aphorisms and epigrams, and his Trivia has been highly rated. He was a literary perfectionist and could take days refining his sentences. With Words and Idioms he became a recognised authority on the correct use of English. He is now probably most remembered for his autobiography Unforgotten Years (1938). He was much influenced by Walter Pater. As well as his employees listed, his followers included Desmond MacCarthy, John Russell, R. C. Trevelyan, and Hugh Trevor-Roper. He was, in part, the basis for the character of Nick Greene / Sir Nicholas Greene in Virginia Woolf's Orlando.