Bittorrent is a new technology that distributes large, popular files over the Internet by organizing the cooperation of simultaneous downloaders. This cooperation alters the behavior of the Internet as a whole. With conventional file tranfer protocols, the throughput of the Internet is bounded by the capacity of file publishers ('producers'); with cooperative file distribution the throughput of the Internet is proportional to the capacity of the downloaders ('consumers'). Cooperative file transfer democratizes publication on the Internet by dramatically lowering cost and bandwidth barriers. The lower costs of distribution are rapidly making it the standard method for on-line publishing of Linux distributions, movies and multi-CD games. Over the last two years more than 60 million Bittorrent clients have been downloaded. The Bittorrent protocol moves more bytes than all other peer-to-peer methods combined, and accounts for more than 1/3 of all the traffic on the Internet. Bittorrent draws on some of the cooperative techniques that enable biological and social communities to function. This talk will examine the algorithms that enable effective cooperation of downloaders. It will also consider the likely social impact of flexible and inexpensive digital distribution channels.