Ashley Olsen's Costume Change

Ashley Olsen picks up a few items while shopping at Costume National in West Hollywood on Thursday.

IS THAT A BIG FAT SMILE I SEE ON HER FACE??

The 21-year-old Olsen twin wore a simple plaid buttondown, skinny jeans and black sandals.

Ashley and sister Mary-Kate‘s stylish coffee-table book called “Influence” will debut this fall.