The semi-finals of March Music Madness are here! That's right: 32 amazing pop songs (that were released some time between the '80s and today) have been narrowed down to the final four, thanks to your votes. Which of these four songs will ultimately win the title of Greatest Pop Song of the Modern Era?

This round is sure to spark some intense fan battles: Will Michael Jackson's 'Billie Jean' beat Britney Spears' 'Baby One More Time'? Will Lady Gaga's 'Bad Romance' top Adele's 'Someone Like You'? Only two of these four songs will move on to the finals, and one of the final two songs will be crowned the winner.

Start voting now! Just click the blue button below. Remember, you can vote up to once per hour until this round is over. Voting in the Semi-Finals ends at 12PM ET on April 1. Finally, the Greatest Pop Song of the Modern Era will be announced on April 8.

After you've voted, don't forget to enter the contest at the bottom of this page to win a $100 iTunes gift card -- our gift to one of our lucky readers for joining in on the fun of March Music Madness.