Lein may refer to:
People with that name Allen Lein (1913–2003), American endocrinologist and medical school professor Anatoly Lein (1931–2018), Soviet-born American chess Grandmaster Lars O. Lein (1874–1958), American farmer and politician Mahide Lein (born 1949), German LGBTQ+ activist Simonetta Lein (born 1983), Italian-American columnist and model
Other Lein (Neckar), a river of Baden-Württemberg, Germany, tributary of the Neckar Lein (Kocher), a river of Baden-Württemberg, Germany, tributary of the Kocher Forbregd/Lein, two small adjoining villages in the municipality of Verdal in Trøndelag county, Norway Leiningen (software), the command lein is used for this packaging software
See also Col du Lein, a high mountain pass in the Alps in Switzerland