BBC News has a report on Access Denied: The Practice and Policy of Global Internet Filtering, a book that blows away the old cliche about governments being unable to censor the internet.
Ronald Deibert, one of the book's editors, says: "What we're finding is that states that were taking a hands-off approach to the internet for many years are now finding ways to intervene at key internet choke points, and block access to information."
Mr Deibert heads The Citizen Lab at the University of Toronto. The Lab, along with Harvard Law School, the University of Cambridge, and Oxford University, has spent the last five years testing internet access in some 40 countries.
Countries such as China, Iran, and Pakistan are well known for net censorship, "But it's not a simple equation with territorial boundaries," says Deibert. "Maybe the best analogy is with the old Middle Ages, where you had multiple and overlapping layers of authority. I think that's the future of the net."
There's a contents list and sample chapters here.
In the UK, of course, we may be less likely to censor sites than to make it a crime to look at them.
