Over 3,000 international investment treaties (IITs) are in force, more are being negotiated. While informed debates on IITs are usually framed in legalistic terms, the signing and wording of these treaties imply important trade-offs between policy goals. The ramifications can be expensive (the record payout to investors for breach of an IIT is US$1.7 billion), far-reaching (affecting issues well beyond investment policy, including public health or environmental measures), and difficult to withdraw from (because
the ability to terminate a treaty or its effects may be restricted for decades). Countries considering negotiating investment treaties need proper reflection and public debate on these policy choices. This overview briefing is the first of four promoting debate on IITs and sustainable development.