The Permesso di Soggiorno (Pds), the permit of stay, is the holy grail of documents. It means you are legal, registered, and entitled to run around the town fountain blind-drunk chanting communist battle hymns. it is obligatory for anyone enrolling in a university course in Italy. If you come from one of the European union countries (as well as Iceland, Norway and Liechtenstein) you still need one although the pre-requisites are only your passport and identity card. Most of these are now done at the Post office. Unfortunately this and registration for the stranieri have gotten so complicated they almost need a chapter themselves. The best thing to do is go online and at the stranieri’s complete instructions on their website.