Happi (法被, 半被) is a traditional Japanese straight-sleeved coat usually made of indigo or brown cotton and imprinted with a distinctive mon (crest).

Happi vests are usually worn on festivals.

Originally, these represented the crest of a family, as happi were worn by house servants.
Later, the coats commonly began to display the crests of shops and organisations.

Firefighters in the past also used to wear happi as marks of masculinity.
The symbol on their backs referred to the group with which they were associated.