259 © Springer Nature Switzerland AG 2019 K. Fach Gómez et al. (eds.), International Investment Law and the Law of Armed Confict, European Yearbook of International Economic Law, https://doi.org/10.1007/978-3-030-10746-8_13 Protection of Foreign Investments Against the Effects of Hostilities: A Framework for Assessing Compliance with Full Protection and Security Ira Ryk-Lakhman Contents 1 Introduction 260 2 Full Protection and Security and Customary Law on the Treatment of Aliens 264 2.1 The Customary Obligation to Take “Reasonable Care” and Its Content 265 2.2 Full Protection and Security Is a Reference to Customary Law 268 3 Full Protection and Security and Customary International Humanitarian Law 271 3.1 The Obligation to Take Feasible Precautions Against the Effects of Hostilities 272 3.2 The Relationship Between FPS and the Obligation to Take Precautionary Measures 275 4 Conclusion 279 References 279 Abstract In recent years there has been an increase in the number of investor-State arbitrations involving war-torn States. Among other issues, the investors in these claims seek redress for the State’s alleged failure to protect against the destruction of property by third parties as required under the “full protection and security” stan- dard. Although this standard appears in most investment instruments, its content and scope is mostly controversial, while its operation against the particular backdrop of armed conficts and international humanitarian law, is completely neglected. This chapter addresses both points of controversy. It is argued that, “full protection and security” imposes a relative due diligence obligation that accounts for the particular circumstances of the host State in the assessment of compliance with the obligation. The law of armed confict, in turn, also imposes a relative due diligence obligation to take “feasible” precautions in favour of foreign investments against the effects of attacks. Assessment of compliance with this international humanitarian law obliga- tion turns on an available means analysis. Both assessments of the applicable due I. Ryk-Lakhman (*) UCL, Laws, London, UK e-mail: ira.lakhman.14@ucl.ac.uk Thank you to Caroline Henckels and William Kent for their comments and to the reviewers for their suggestions.