This book is my doctoral dissertation, which I defended at the Department of Law at the European University Institute in Florence, Italy. I would like to thank the Danish Rectors' Conference, which sponsored my three years at the European University Institute. I would also like to express my great appreciation to the members of my committee: Dr. Christine Gray from Cambridge University, Professor Francesco Francioni from the European University Institute and Professor Natalino Ronzitti from LUISS University. My special thanks goes to my supervisor, Professor Philip Alston from New York University.