Rome Convention
Article 12
Voluntary assignment
1. The mutual obligations of assignor and assignee under a voluntary assignment of a right against another person ('the debtor') shall be governed by the law which under this Convention applies to the contract between the assignor and assignee.
2. The law governing the right to which the assignment relates shall determine its assignability, the relationship betweeen the assignee and the debtor, the conditions under which the assignment can be invoked against the debtor and any question whether the debtor's obligations have been discharged.