This Practice Note provides an introductory overview of investor-state arbitration and the key protections offered by bilateral and multilateral investment treaties (BITs and MITs) in respect of investments in foreign states. It sets out an explanation of the kinds of protections afforded to investors under those treaties and how investment disputes are resolved. It gives an outline of common issues in investment treaty arbitration, including who is an investor, what is an investment, jurisdiction, negotiations, interim measures, enforcement and state immunity. It provides an introduction to the International Centre for Settlement of Investment Disputes (ICSID) and to other arbitral bodies which administer proceedings in investment treaty arbitrations.