Harenchi Gakuen (ハレンチ学園, lit. "Shameless School") is a Japanese manga series written and illustrated by Go Nagai. The manga was one of the first to be serialized in Shueisha's shōnen manga magazine Weekly Shōnen Jump, where it ran from 1968 to 1972, with its chapters collected in thirteen tankōbon volumes. A modern-day version of the manga, Heisei Harenchi Gakuen, was serialized by Nihon Bungeisha and Jitsugyo no Nihon Sha in Weekly Manga Goraku and Weekly Manga Sunday, respectively, from 1994 to 1995. A sequel to the original series, illustrated by Teruto Aruga and titled Harenchi Gakuen: The Company, was serialized in Shueisha's Business Jump from 2007 to 2008.

Harenchi Gakuen was adapted into four live-action films and a twenty-seven-episode Japanese television drama. Heisei Harenchi Gakuen was adapted into a direct to video live-action film and an original video animation (OVA).

Harenchi Gakuen became the first big success for Nagai and is widely considered the first modern erotic manga and credited for being the first ecchi manga series.