International policy-makers so far have successfully pre-empted any new major national legislation in the G7 countries aimed specifically at sovereign wealth funds by getting the International Monetary Fund to work with them on formulating a set of best practices commonly known as the Santiago Principles. However, some observers stress that this is just the beginning. How does one measure and evaluate compliance with these principles? Is voluntary self-regulation really sufficient? Or is there a need for new rules and regulations? As the discussion shifts from policy and economics to governance and regulation, we move firmly into the realm of law—legal norms, rules, and statutes. However, the required clarity and commonality of definitions and terms have been elusive. There does not seem to be universal agreement about the precise meanings of even the most fundamental terms in the SWF debate. This article hence focuses on the definitional challenges inherent in this debate.