In Parenthesis (published in the United Kingdom in 1937) is an epic poem in novella form by David Jones. The epic prose-poem tells the story of Private John Ball and his unit's war experience in World War I, starting with their military training in England and ending with the Battle of the Somme, and a mediation on history and legend. T. S. Eliot has called it, "a work of literary art which uses the language in a new way."

Jones worked on the novel for ten years. He uses modernist writing techniques in combination with British literary allusions to hint at a connection between World War I and the heroic wars of the English and Welsh past. The poem draws on literary influences from the 6th-century Welsh epic Y Gododdin to Thomas Malory's Le Morte d'Arthur to try to make sense of the carnage he witnessed in the trenches.

David Jones CH (1 November 1895 – 28 October 1974) was both an artist and one of the most important first generation British modernist poets. His work was formed by his Welsh heritage and his Catholicism. T. S. Eliot considered Jones to be a writer of major importance and his The Anathemata was considered by W. H. Auden to be the most important long poem written in English in the 20th century.