Beyonce's Soulful Birthday

When Beyonce wants her guests to rock 1970s getups for her birthday ... best believe they fall into formation.

Queen Bey turned 35 over the weekend, but come Monday, she threw herself a Sooouuuuuul Train-themed rooftop party at The Nomad Hotel in NYC. All the celebs in attendance turned out in '70s gear ... and then hit the dance floor to get their groove on.

Some of those stars included Diddy and Cassie, Kendrick Lamar, Usher, Michelle Williams, Kelly Rowland and Alicia Keys. And, of course, Jay was by her side gettin' down.

Bey was the true star of the show though, reminding everyone who they were celebrating.