This paper reviews alleged societal benefits and costs of International Investment Agreements (IIAs) as suggested by academia, governments, business and civil society. It sets out the wide range of issues that diverse actors have proposed in the context of assessing the societal benefits and costs of IIAs. The paper analyses and organises the available material generated by these sources to identify and classify the many different issues, summarises available empirical evidence and findings in these sources on the individual aspects, and assesses strengths and weaknesses of the approaches. The paper focuses in particular on the investor protection component of IIAs. The inventory finds that for many claims about the positive or negative impact of IIAs, little robust evidence has been generated to date. The paper highlights methodological challenges and suggests areas where further study would be required to draw firmer conclusions.