Sexy Britney Spears Stage Pictures

Britney Spears turns 31 today! The singer has brought plenty of hotness since hitting the scene in 1999, including endless amounts of ab-baring ensembles and multiple envelope-pushing dance moves. Britney's new role as an X Factor judge and mentor has her hitting the stage in a different way, but her star presence and sex appeal are as hot as ever. We're celebrating Britney's big day with a look back at her steamiest stage moments, from sexy schoolgirl to circus ringleader to full-blown femme fatale. Click through to see them all now!