This project would not have been completed without the support and assistance of a number of institutions and individuals. I thank the University of Sheffield School of Law for providing me with the necessary resources to produce this monograph. I also extend my gratitude to the NATO Cooperative Cyber Defence Centre of Excellence in Tallinn, Estonia, for hosting me during my sabbatical in late 2016. The Centre provided me with a warm and intellectually rich environment to pursue my research. This monograph has benefited from the many deep and stimulating conversations that I have had with Iñaki Navarrete on the topic of international law and espionage, which I enjoyed immensely. I thank Iñaki for assisting me with the research for chapter 5 of this monograph and I also thank Adam Keenaghan for meticulously editing the final manuscript. I am indebted to Cormac Behan, Patrick Capps, David Hayes, Clair Gammage, Tarcisio Gazzini, Gregory Messenger and Nicholas Tsagourias for reading through various chapters of this monograph and providing useful comments. On a personal level, I am grateful for the love and support of my husband, Shane, and I apologise once again for the many early mornings, late nights and lost weekends that you had to withstand during the course of this project. Finally, this monograph is dedicated to Juanita Patrick: your love, humour and happiness are dearly missed and we think about you every day.