When Swedish public bodies have reasons to contact and co-operate with foreign public bodies, this may give rise to legally complex situations. There are reasons to endeavour to seek solutions adapted to the needs of each individual case. This thesis investigates legal frameworks for such solutions. The investigation in particular deals with binding agreements concluded by Swedish public authorities and municipalities with corresponding types of foreign public bodies. By the conclusion of such agreements more than one legal system may be involved. This thesis deals with Swedish national law and public international law. A question of central concern for this thesis is to what extent it is possible for a Swedish public body to regulate co-operation by means of a binding agreement. It is concluded that the possibilities are relatively good. A condition for this is, however, that the agreements in questions are not subject to the provisions in the Instrument of Government (Chapter 10) on international agreements. These provisions are applicable to binding agreement under public international law and arguably also to certain agreements regulated by rules of other legal systems. Another question of central concern for this thesis is which terms may be included in cross-border co-operation agreements; regulation set up limits on the matters for which public authorities may enter into agreements. These limits affect among others agreements that would have effects on foreign policy or that would transfer the right of decision-making. In addition to these two questions, this thesis, among other questions, deals with the choice of legal system regulating a cross-border agreement and legal effects of ultra vires agreements.