The definition of investor and investment is key to the scope of application of rights and obligations of investment agreements and to the establishment of the jurisdiction of investment treaty-based arbitral tribunals. This factual survey of state practice and jurisprudence aims to clarify the requirements to be met by individuals and corporations in order to be entitled to the treatment and protection provided for under investment treaties. It further analyses the specific rules on the nationality of claims under the ICSID Convention. As far as the definition of investment is concerned, most investment agreements adopt an openended approach which favours a broad definition of investment. Nevertheless recent developments in bilateral model treaties provide explanatory notes with further qualifications and clarifications of the term investment. The survey further reviews the definition of investment under ICSID as well as non-ICSID case-law for jurisdictional purposes.