Art. 111(2) EPC provides that, where a board of appeal remits a case to the EPO department of first instance whose decision was appealed, that department is bound by the board's ratio decidendi, in so far as the facts are the same. If the decision under appeal was taken by the Receiving Section, the examining division is also bound by the board's ratio decidendi.

The boards' decisions generally acquire the authority of "res judicata" on being issued. "Res judicata" is a generally recognised principle in the contracting states that is acknowledged by the boards of appeal (see e.g. T 167/93, OJ 1997, 229; J 3/95 date: 1997-02-28, OJ 1997, 493; T 365/09, T 449/15). It means a matter finally settled by a court of competent jurisdiction, rendering that matter conclusive as to the rights of the parties and their privies, such a final judgment constituting an absolute bar to a subsequent legal action involving the same claim, demand or cause of action, and the same parties or their privies (T 934/91, OJ 1994, 184; see also T 1666/14).

A decision's binding effect under Art. 111(2) EPC applies only to the case decided on (J 27/94, OJ 1995, 831). Art. 111 EPC does not provide for such binding effect for cases not decided by the boards, although there will generally be good reasons for departments of first instance to follow their decisions in order to maintain a consistent practice and avoid unnecessary appeals.

The authority of res judicata binds the administrative department dealing with the same application in the subsequently resumed examination proceedings (see Art. 111(2) EPC) and indeed the board in any fresh appeal against the then ensuing examination decision. By contrast, a decision taken on appeal in examination proceedings has no such binding effect in any subsequent opposition proceedings or on appeal against the opposition division's decision because opposition proceedings are separate and distinct from examination proceedings (especially in that different parties are involved) and differ from them in terms of the nature of the public interest involved (T 1666/14).

The ratio decidendi of a decision under Art. 111(2) EPC 1973 is the ground or the reason for making it – in other words, the point in a case which determines the outcome of the judgment (T 934/91, OJ 1994, 184). It is not contained in the order but in the section "Reasons for the Decision" and it is thus of no importance for its binding effect that a particular matter is not mentioned in the order (T 436/95). The order of a board's decision provides a first point of reference for establishing the extent to which res judicata applies. However, where a case is remitted for further prosecution on the basis of claims of auxiliary requests following rejection of higher-ranking claim requests, the order is usually confined to the setting aside of the decision under appeal and the remittal for further prosecution. Thus, the order has to be seen in context with the reasons for the decision as a whole in order to determine the extent to which the decision is final (T 449/15).