When the Gregorian calendar was adopted in the 1500s, many people did not immediately receive word that New Year's Day had been moved to January 1st.  They continued to celebrate as usual, at the end of March, for 8 days.  Eventually, most accepted the reformed calendar, but there were a few stragglers who either lived in relative isolation or else held stubbornly to past practice and continued celebrating New Year's in Spring.  These anomalous curiosities and stodgy holdouts were labeled fools by everyone else, were subject to ridicule and practical jokes, and hence the April Fool's tradition was born. 

April Fool's Day is for fun only.  We don't send cards, buy presents, or get a day off work, but it's still imperative to plan ahead if you want to take full advantage of the holiday.  Here are a few books to get you in the mood for whatever April Fool's Day holds in store.

Image courtesy of Enrico Webers