Discovered recently, K2P potassium channels (encoded by KCNK genes) are numerous, widespread and notable for their unique structure: each subunit possesses two pore-forming P domains. The channels are also remarkable in function, serving as highly regulated, potassium-selective leaks. Fundamental to the excitability of nerves and muscles, the molecular basis for leak currents had previously been a mystery. Channels in-hand, we can now consider why they remained hidden and the structural basis for their operation. Many of our most basic questions remain to be answered.