This is the long-awaited second edition of this widely-referenced work on the substantive law principles of investment treaty arbitration. It forms a detailed critical review of the substantive principles of international law applied by investment arbitration tribunals, and a clear and comprehensive description of the present state of the law. The first edition met with immediate success as a result of the authors' achievement in describing and analyzing the volume of law created, applied and analyzed by tribunals. The second edition is fully updated to take account of the arbitration awards rendered in the period since 2007. Written by an internationally recognized author team, it is now the most comprehensive and up to date work in its field and no practitioner or academic can afford to be without it. Key areas of coverage include: the instruments under which investment disputes arise; the legal basis of treaty arbitration; dispute resolution and parallel proceedings; who is a foreign investor, including nationality issues and foreign control; what is an investment; investors' substantive rights, including fair and equitable treatment; expropriation; compensation and remedies.