The following Oxford Bibliographies Online contains very useful lists of books, journals and journal articles, as well as some primary sources, and are an excellent place to start your research into international investment law. These Bibliographies are all in the Oxford Bibliographies International Law module.
Foreign Investment - by Nicolas Angelet & Mathilde Rousseau
Investment Protection Treaties - by Silvina Gonzalez Napolitano
International Investment Arbitration - by C.L. Lim & Jean Ho