is a comedy manga, written by Sasaki Mutsumi and illustrated by Shinnosuke Mori, serialized in Dengeki G's Magazine
from April 1999 to September 2002, featuring a high school student who is adopted by five of his teachers. It was adapted into a five-part OVA series in 2001; a thirteen-episode animated TV series in 2002; a sequel TV series, called Happy Lesson Advance
, in 2003; and a second OVA series, Happy Lesson: The Final
, in 2004. The series has also been adapted into a series of drama CDs and a Dreamcast game.
The first volume of the manga was licensed and released by A.D. Vision's ADV Manga label in the United States; the first three episodes of the OVA and the first TV series were licensed by the ADV Films label for Region 1 distribution.