This paper considers what the archival material of the 14th and 15th centuries can tell us about this question: how and to what extent the rights of the inhabitants of certain northern Italian cities (Ferrara, Cremona, Padua and Venice) were protected if their property was located in foreign territory and/or their property interests could be restricted by the power structures of another Italian centre. The first problem concerned the property of the Church. A study of the documentary material shows that one way of preserving the property of the Church on foreign territory, despite the increasing tendency of secular rulers to seize church lands, was to place it in possession of the local population on a secure basis - emphyteusis, livelles, or other type of long-term use. The second problem was enforcing the contracts, i.e. suing the party which had not fulfilled or improperly fulfilled their terms if the infringer was on foreign soil. The records show that this was most probably enshrined in agreements between the Italian city-states and was incorporated by means of a special formula in the treaties. The third problem was related to the property rights of the inhabitants of medieval Italy, whose real estate, together with the territory in which it was situated, passed under the jurisdiction of another ruler. A study of the lettere ducali shows that such legal relations were based on treaties between the rulers of Italian territorial states and became the subject of diplomatic correspondence