We shall explain the renewed interest in mix networks. Like Tor, mix networks protect metadata by using layered encryption and routing packets between a series of independent nodes. Mix networks resist vastly more powerful adversary models than Tor though, including global passive adversaries. In so doing, mix networks add both latency and cover traffic. We shall outline the basic components of a mix network, touch on their roles in resisting active and passive attacks, and discuss how the latency impacts reliability, application design, and user experience.