Cass Timberlane is a novel by Sinclair Lewis, published in 1945. The book is set in the fictional town of Grand Republic, Minnesota, and tells the story of a middle-aged judge named Cass Timberlane and his romance with a young socialite named Jinny Marshland.

Cass is a respected member of the community, but he is lonely and dissatisfied with his life. When he meets Jinny, he is immediately drawn to her youthful energy and beauty. Despite their age difference and the disapproval of their friends and family, Cass and Jinny begin a passionate romance.

However, their relationship is complicated by Jinny's past, which includes a failed marriage and a scandalous affair with a married man. Cass struggles to reconcile his love for Jinny with his sense of propriety and his duty to uphold the law.

The novel explores themes of love, morality, and social class, and is considered one of Lewis's more sentimental works. It was adapted into a film in 1947, starring Spencer Tracy and Lana Turner.