The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

Abstract Over the last decade, Investor-State Dispute Settlement (ISDS) has been the most controversial issue in international investment law and policy. This paper is not intended to take sides with any position on the multiple dimensions of the ISDS debate. Instead, this note only attempts to examine and summarize the empirical evidence available which may be useful to foster a more factual and objective discussion on this controversial topic. To achieve this objective, this note will empirically assess the use of ISDS between 1987 and 2017 by focusing on eight key questions: (i) the number of ISDS disputes; (ii) the most commonly used arbitration rules, venues and arbitrators; (iii) the features of the parties involved in disputes -both investors and States; (iv) the investment protection guarantees most frequently invoked by investors and the most frequently recognized by tribunals; (v) the economic sectors in which ISDS tends to concentrate, (vi) the outcomes of the disputes, (vii) the performance of the ISDS procedures in terms of time and cost, and (viii) the frequency of ISDS relative to State-to-State investment dispute settlement. This evidence summarized in this paper shows that ISDS is a manifestation of deeper and more complex political economy in the relationship between foreign investors and host States. The debate on ISDS has deviated the attention from a more critical issue. That is, the significant number of cancellations or total withdrawal of investment projects in developing countries and economies in transition that never reach ISDS, and yet entail the same type of grievances that IIAs are supposed to prevent. This finding suggests that in practice, in many countries the principles and disciplines included in IIAs are not being fully implemented nor mainstreamed within regular administrative action at different levels of government.

Whilst the principle of proportionality indisputably plays a crucial role in the protection of fundamental rights, it is still unclear to what extent it applies to other fields in international law. The paper therefore explores the role it plays in selected fields of public international law, beyond human rights. The examination begins in the classical domain of reprisals and in maritime boundary delimitation and continues to analyse the role played in the law of multilateral trade regulation of the World Trade Organization and in bilateral investment protection. In an attempt to explain differences in recourse to proportionality in the various fields, we develop in our conclusions a distinction between horizontal and vertical constellations of legal protection.

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