This Chapter deals with the treatment of third States in maritime delimitation jurisprudence. It first examines the ways in which delimitation decisions may impact third States, in particular States which have overlapping claims with one or both parties to a delimitation case. In this context it considers whether a delimitation decision may be considered as having erga omnes effects, despite the fact that decisions of international courts and tribunals are, in theory, only binding on the parties to a case. It concludes that a delimitation decision can have a determinative effect in certain circumstances. The Chapter also considers the ways in which courts and tribunals have dealt with third States issues. It examines the techniques used by courts and tribunals in order to take overlapping claims of third States into account, such as delimitation without a fixed endpoint. It also considers whether the presence of third States may constitute a relevant circumstance in the context of the standard three-step delimitation methodology. An analysis of the jurisprudence indicates that the driving factor behind the approach of courts and tribunals to the issue of third State interests is the desire to ensure the stability and finality of the boundary delimited.