As red carpets go, Cannes is definitely one of the most formal — they banned group selfies this year and heels are supposedly mandatory for girls. Essentially, the South of France's Côte D'Azur turns into one big sea of ball gowns for a week, with a few movies thrown in. And you know you can count on Sienna Miller, Rooney Mara, Natasha Poly and the rest of this gang to bring the high-glam hair for the occasion. (Did someone say wedding season inspiration?)