In this paper we propose a new structured overlay network, which is more efficient and scalable than previous ones. We call it Twins, because its routing table consists of two parts, one containing nodes with common prefix and the other containing nodes with common suffix. Twins routes messages to their destinations in just 2 hops even in a very large scale and the overhead is very low. When deployed in a peer-to-peer system with 5 000 000 nodes, each node receives only 6 messages per second for routing table maintenance. This cost, as well as routing table size, varies as a O(sqrt N) function to the overlay scale, so Twins can also run well in an even larger environment.