Do remember which songs were at the top of the charts 10 years ago [1]? Some of the hits included "California Gurls" by Katy Perry [2], "Hey Soul Sister" by Train, and "Bad Romance" by Lady Gaga [3], but none of those songs claimed the top spot on Billboard's year-end charts. In fact, some of today's biggest artists — Drake [4], Ariana Grande [5], Billie Eilish [6], and Khalid [7] — weren't even able to secure this honor. Who has been anointed Billboard's Hottest Song of the Year? Let's take a trip down memory lane and reminisce about the 10 most popular songs of the decade.