The 'Gone Girl' actress went for a red Givenchy gown, sweeping her hair back into a simple bun.
Rosamund is nominated for the Best Actress award, for her role in 'Gone Girl'.
Red was the order of the day...
Other stars who wowed on the red carpet include Lupita Nyong'o, who stunned in a custom Calvin Klein gown, adorned with 6000 pearls.
Lady Gaga also turned heads, though her gloves weren't exactly a hit...
Who else impressed us with their style choices? And who should sack their stylist? Check out all the red carpet snaps below...
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