In New York City and other fashion capitals, one unusual breed of shoe is turning up over and over: Sock sneakers. Typically just a minimal, stretchy knit upper and a sole, sock sneakers originated with big athletic brands. But luxury labels have since eagerly taken up the thread, pushing the form to deliberately emphasize the resemblance to socks. In the normal course of fashion’s trend cycle, mass-market brands have begun copying them and producing their own versions too. They now exist in seemingly endless iterations across a variety of price points, and embody some of the big currents moving fashion today.