Stefani joined Pharrell onstage for a performance of her 2004 smash, "Hollaback Girl," which she co-wrote with Williams and his Neptunes collaborator Chad Hugo.
"Feels good to be out of the cave #Cochella2014 @Pharrell gx," the No Doubt frontwoman tweeted.
Diplo, Nelly, Snoop Dogg, Puff Daddy also made appearances.
You can watch the full set below:
Swim Week Miami Beach 2014 [PHOTOS]