Traditionally, the choice of an interpretive method and practice is contingent upon the governing law and nature of the agreement under scrutiny. In this respect, international commercial and investment tribunals have significantly contributed to shaping the pivotal role of legal interpretation within the parameters of international adjudication.

It is now undisputed that the internationalization of wide-ranging economic activities and the emergence of State contracts have reshaped the classic distinction between contracts and treaties, and softened the sharp dichotomy between the national and international orders. Despite the straightforwardness of the distinction between contract and treaty in principle, it is also evident that the distinction is not so clear-cut in practice and international arbitral tribunals are often asked to resolve disputes involving these two types of instruments. This practice has rendered it more difficult to separate the issue of interpretation from that of applicable law.

This entry’s point of departure is an analysis of the scope of the rules of interpretation in light of the growing overlap between legal orders, treaties and contracts. Engaging in a comparison of the methods of interpretation in contracts and treaties, the authors then examine the arbitrators’ gap-filling power when facing an ambiguous term or silence. Arbitral tribunals’ use of aids to interpretation and extrinsic evidence or ‘supplementary means’ to interpretation are also discussed.

The International Law Commission has described the operation of the VCLT rule of interpretation as a ‘crucible’, whereby it is the combination of the interpretative principles contained in the VCLT rule that in each case yields the meaning of treaty provisions. Taking that view as its starting point, Chapter 4 points out that different interpretative VCLT principles may be assigned different weights in different cases, depending on the drafters’ constructed intention followed by the adjudicator in each case. The underlying idea, therefore, is that all these interpretative principles must hang together well and must be combined in a way that makes sense in the context of each case. This is a sign that considerations of coherence are apposite in the operation of the VCLT rule, acting as reasons that justify the above combination in each case and ultimately account for the outcome’s persuasiveness. In the process, the chapter identifies two key coherence-related processes: framing and normative contextualisation

This chapter addresses the challenges arising from the often unclear legal status of intra-state peace agreements in establishing their binding force, applicable law and relevant principles of interpretation, and considers how drafting techniques affect the implementation of such agreements. First, it maps out the means available to participants in a peace process to confer binding status on (the substance of) an agreement under either domestic or international law, including UN Security Council endorsement, domestic entrenchment or constitutional reform. Second, the chapter examines how (predominantly international) courts and tribunals have grappled with the task of determining the law applicable to peace agreements, as well as examining trends in the principles of interpretation applied by adjudicatory bodies. Finally, it turns to the effects of drafting techniques on the implementation of agreements from the perspectives of the constitutive and instrumental approaches, including weighing the merits of constructive ambiguity.

While third states and international organisations often co-sign peace agreements in the capacity of witnesses or guarantors, little is understood of the legal consequences flowing from these roles. The chapter aims to fill this gap. First, it highlights that the mere designation of witness or guarantor leads to few consequences. Second, it analyses how specific third-party rights and obligations are established and conceptualised under VCLT rules, extended by analogy to intra-state peace agreements. Third, it provides a brief illustration of common third-party rights and obligations in peace agreements. Finally, it examines whether the involvement of third parties can internationalise an intra-state peace agreement, i.e. render it to be governed by international law. Bringing together views from the literature, jurisprudence and the preceding analysis on the structure of third-party rights and obligations, the chapter concludes that such rights and obligations can be internationalised, in a manner that can only extend to the agreement as a whole when inseparable from the rest of the agreement.

While third states and international organisations often co-sign peace agreements in the capacity of witnesses or guarantors, little is understood of the legal consequences flowing from these roles. The chapter aims to fill this gap. First, it highlights that the mere designation of witness or guarantor leads to few consequences. Second, it analyses how specific third-party rights and obligations are established and conceptualised under VCLT rules, extended by analogy to intra-state peace agreements. Third, it provides a brief illustration of common third-party rights and obligations in peace agreements. Finally, it examines whether the involvement of third parties can internationalise an intra-state peace agreement, i.e. render it to be governed by international law. Bringing together views from the literature, jurisprudence and the preceding analysis on the structure of third-party rights and obligations, the chapter concludes that such rights and obligations can be internationalised, in a manner that can only extend to the agreement as a whole when inseparable from the rest of the agreement.

This chapter tackles the issue of interpretation from the point of view of motion and time, mainly motion as change in space-time (kata topon kai chronon metavole), which depending on the interpretation could lead to an increase (auxesis), diminution (meiosis) of the treaty. This is mainly evidenced through the concepts of the principle of contemporaneity and evolutionary interpretation, and the chapter proceeds to demonstrate that the choice between these two is dependent on the ‘time-will’ of the parties. However, even evolutive interpretation has its limits and should never lead to an alteration (alloiosis) of the treaty. This chapter also analyses the rules of interpretation themselves, ie whether interpretative rules are constants, immutable and perennial ones, in the system of the law of treaties or whether they are, as any other rule, potentially susceptible to motion through time and change. This chapter demonstrates the false premise of the immutability of the rules of interpretation, and elaborates on the consequences of this to the choice between contemporaneous (static) and evolutive interpretation.