Poisson d'Avril: April Fool's Day Tradition in France

Poisson d'Avril - France's April Fool's Day Tradition

I love learning about different traditions celebrated in other countries. When I first heard how the French celebrate April Fool's Day I was quite confused. The day is called Poisson d'Avril and the tradition is to tape a paper fish drawing on to your friend's back without them knowing. It has the same light hearted silliness as a prank one might play on April Fool's Day in the United States, but the prank never changes. It's always a fish. So, why the name "April fish" and how did the tradition come to be?