The Dutch Supreme Court recently ruled that a party, which had not been a party to the proceedings in the lower courts, could be joined to appeal proceedings to the Dutch Supreme Court.

This ruling was received with some surprise as, in earlier decisions, the Supreme Court had ruled that intervention in appeal proceedings (whether by a joinder of parties or third party intervention) was generally not permissible.

It follows that a party can now join another party in appeal proceedings to the Dutch Supreme Court, providing the "incoming party" can show it has an "interest" in joining the litigation. To demonstrate such interest, it is sufficient that an outcome which was unfavourable for an existing party to the litigation adversely affects the legal position of the incoming party. The incoming party is, however, bound by the grounds for appeal put forward by the existing party and cannot present fresh grounds for appeal itself (even when the period for bringing an appeal to the Supreme Court has not expired yet).

The ruling of the Supreme Court will be of practical interest for various organised interest groups. For instance, in appeal proceedings to the Dutch Supreme Court between a listed company and a (major) shareholder, interest groups which are founded to protect shareholders' interests in general could join the other shareholder in the litigation. It goes without saying that this would apply equally for other stakeholders.