To help celebrate, Happify.com has created this infographic on the "science of happy."
At 24 Hours of Happiness, Williams is showcasing his favorite videos that people have uploaded with the hashtag #gethappy. He's picking one every hour until the day's done.
While you're at it, though, you should probably watch this amazing cover of "Happy" by the Detroit Academy of Arts and Sciences choir. In an already crowded field of "Happy" covers, it's a shining star.