The origins of April Fools' Day, or All Fools' Day as it's sometimes known, is a little murky but it seems it may have originated around 1582 in France.
This was the year the Gregorian calendar was introduced and celebrating the new year changed from April 1st to January 1st. It's claimed that some of the locals, out of ignorance or sheer stubbornness continued to ring the town bell on April 1st to mark the New Year, hence the term "April Fool" was born.
Nowdays, the tradition has evolved into a day where we can play harmless pranks, create hoaxes or play practical jokes on friends, family & co-workers. Even the mass media have constructed elaborate hoaxes for viewer consumption and entertainment.
Beware the April Fool!
The History of April Fools' Day
April Fools' Day: Origins & History