According to the Federal Constitution, concluding international agreements is the prerogative of the Confederation, but the cantons may conclude treaties with foreign states on matters that lie within the scope of their powers. Swiss law requires the Confederation and the cantons to collaborate closely on cross-border matters. The cantons may deal directly with lower-level (local or regional) authorities e.g. to deal with specific problems shared by neighbouring regions.
However, the cantons may not deal directly with central government authorities of foreign states. The Federal Constitution provides that official contacts take place via the Federal Council. It is therefore up to the Federal Council to conduct negotiations and to sign and ratify the agreement. Although the Federal Council acts at the request and on behalf of the cantons concerned, it also takes account of the interests of the Confederation and of other cantons.
The Federal Council usually concludes agreements on behalf of the canton. The canton is the contracting party, so the agreement must be approved in accordance with cantonal procedures. If it is in the direct interests of the Confederation, however, the Federal Council can also conclude agreements on it own behalf.