Slip dresses have become a wardrobe essential over the past few years, the '90s and '00s staple having had a contemporary refresh. Tartan and lace was worn by everyone from Gwen Stefani to Courtney Love back in the riot grrrl days, while Jennifer Aniston made a great case for mules and a simple slip in the early 2000s. Now, the oh-so-easy dress is taking our wardrobes seamlessly from a wrapped-up winter (worn over roll necks and tights) to the height of summer.