Fashion collaborations long ago became a fixture of the retail calendar – to varying degrees of success. At their best, they bring together complementary strengths: a designer's distinctive point of view, a retailer's reach, or a heritage brand's expertise. This summer's standout collaborations do just that, whether it's Cecilie Bahnsen bringing her romantic aesthetic to UNIQLO or Caramel London lending a touch of quiet luxe to Zara. These are the partnerships worth a closer look.