The twin-arginine translocation (Tat) system, found in prokaryotes, chloroplasts, and some mitochondria, allows folded proteins to be moved across membranes. How this transport is achieved without significant ion leakage is an intriguing mechanistic question. Tat transport is mediated by complexes formed from small integral membrane proteins from just two protein families. Atomic-resolution structures have recently been determined for representatives of both these protein families, providing the first molecular-level glimpse of the Tat machinery. I review our current understanding of the mechanism of Tat transport in light of these new structural data.