(CNN) -- There are happy songs -- and then there is "Happy."
The bouncy tune by singer/composer/producer/rapper Pharrell Williams has occupied the No. 1 spot on the charts for more than a month.
It's spurred countless covers -- including one by Academy Award-winning actress Gwyneth Paltrow, reprising her guest star role in the 100th episode of "Glee."
There is even a YouTube version of "Happy" that has gone completely to the dogs.
What is it about this song, which is so infectiously enjoyable that Meryl Streep had to shimmy to it when Williams performed at the Oscars?
Is it the catchy melody? Is it the insistent nature of such lyrics as "Clap along if you feel like happiness is the truth"? Is it that extra bounce you feel when the back up singers airily croon "Because I'm happppppyyyy"? Or is it the joy of watching Williams and several other folks dance, bounce and lip-sync along with the song in the music video?
Simply put, the song is all those things, even as it has managed to seemingly capture the rush of happiness in its lyrics and melody.
Not a bad trick for a tune that slowly grew from a single on last summer's "Despicable Me 2" soundtrack to such popularity that Robert Morast, a writer for the Virginian-Pilot, recently entered into a debate of whether it should be considered for the official state song of Virginia.
"Pharrell's hit track is a jolt of mood-lifting music," wrote Morast, who was more partial to the Carter Family's "Can the Circle Be Unbroken." "And while it's fine to be happy, the best art is crafted with a range of emotional perspectives."
Even with its slow build, "Happy" caught ears from the beginning. Upon release it was quickly dubbed "an instant contender for 2013's Song of the Summer" by Rolling Stone. Since then, it's topped the charts in more than a dozen countries besides the United States, including the United Kingdom, France, Germany and Poland.
Violinist Lindsey Stirling, who's worked with John Legend and mixes classically styled music with electronic dub-step beats, asks simply, how "can you not love ('Happy')?"
"I was with a friend, and when ('Happy') came on, her baby started kicking and trying to dance," Stirling said. "We were laughing hysterically and saying 'Even babies love this song.' "
She said she believes the reason "Happy" is so beloved is because of its uplifting message.
"I get so excited when something this positive goes this big," said Stirling, whose album "Shatter Me" will be released at the end of April. "It's spreading good feelings and isn't at all controversial. It's just something that is making people really happy."
Williams has partnered with the United Nations Foundation in celebration of Thursday's International Day of Happiness, encouraging fans to donate to the organization and submit content to his 24Hoursof Happiness.com site.
Visitors were asked to tag their submissions, be they dancing, singing or just "being happy" with the #HappyDay. At noon Thursday, in each time zone around the world, Williams will highlight some of the best.
"Happy" is also one of the lead singles on Williams new album "Girl," which has already shot to No. 1 in almost 80 countries and on streaming music giant Spotify. The singer is overwhelmed by the goodwill.
"This is probably the most I've ever been humbled in my entire life," Williams told the Los Angeles Times about his song and the reaction to it. "Because it's something bigger than me, bigger than anything I've ever done."
No doubt that makes him happy.