Sienna attending parties in Chanel. She looks amazing in both dresses, but I esp like the green one.
The black dress fits her so well. It's such a classic yet not boring cut. And that studded clutch def adds a bit of edge to the outfit.
Sienna looked really elegant and cool (and practical) at Sundance in this grey trenchcoat.
At one of the many Factory Girl premieres. This dress is simple, but I'm not sure the cut looks that great on her.
Sienna at another Factory Girl premiere, but this time she looked pretty in this white dress (head-to-toe in Burberry.) I love the details of the dress, like the silver strands that move with her -they totally add life to the dress.
These shift dresses look absolutely fabulous on her. The left photo is of her at the UK Factory Girl premiere. I love that dress: the beaded sequins, and the black hems that balance the overly-cutsy feel of white. (I read somewhere it's vintage Balenciaga.) That black dress on the right is also so perfect for a night event. 
A simple outfit for the CK In2U event. Now this is one outfit we can take notes on because it's actually achieveable for us normal people. It's very 'now'.OK, onto some more 'casual' outfits. Of course, Sienna's casual outfits are not quite your average casual outfit nowadays.
Sienna out for lunch in the simple dress (left) and out for a night out (right). Love the night time outfit. And note the double thin headbands -very 'in' at the moment.
Not a big fan of this daytime look. It just looks too... formal and dressed up, unless she was attending some formal tea party. 
Sienna is more glamourous than boho these days, and she certainly looks glam here. Styling tips for a cold night: wear a sweater under a coat. Sounds like a no duh advice, but most ppl usually freeze on a night out instead of wearing layers.Ahh, if only designers sent clothes to us like they do to Sienna!
