What is the Origin of April Fool's Day ?

This holiday is also known as "All Fool's Day". "April Fool's Day seems to have begun in France in 1564. April 1 used to be New Year's day but the New Year was changed to Jan 1 that year. People who insisted on celebrating the "old" New Year became known as April fools and it became common to play jokes and tricks on them."

SOURCE: Chase's 2006 Calendar of Events   p. 200