There’s a lot of disagreement about the extent to which the state is entitled to take metadata on whom people communicate with on the internet and over the phone. I’d like to make a broad argument, one that I think ought to hold no matter what kind of state you live in, whether you’re in the US or Europe or China or what have you. This argument relies on our conception of the “public network”. What do we understand to be a public network, and what can the state do with public networks? Once we have determined what a public network is, we can apply the same moral and legal principles to every public network. I think that roads, rails, phone lines, power lines, pipes, the internet, and mobile phones are all in an important sense public networks, and that the laws and principles governing surveillance of any one of these networks should apply to all of them.