What do the Department of Defense and the Electronic Frontier Foundation have in common? They have both funded the development of Tor (torproject.org), a free-software anonymizing network that helps people around the world use the Internet in safety. Tor's 1500 volunteer servers carry traffic for several hundred thousand users including ordinary citizens who want protection from identity theft and prying corporations, corporations who want to look at a competitor's website in private, law enforcement and government intelligence agencies who need to do operations on the Internet without being noticed, and aid workers in the Middle East who need to contact their home servers without fear of physical harm. We'll give an overview of the Tor architecture, and talk about why you'd want to use it, what security it provides, and policy and legal issues. Then we can open it up for discussion about open research questions, wider social implications, and other topics the audience wants to consider.