A foreign investor may be displeased when a state discloses, uses or regulates their trade secret. British investors in the Czech Republic and Kenya have acted on that displeasure by bringing claims against those states under investment promotion and protection treaties. While the protection of trade secrets has been noted by commentators, there is yet to be a detailed analysis of the protection of trade secrets under international investment law. To carry out that analysis, I focus on two model United Kingdom treaties and the Comprehensive and Progressive Agreement for Trans-Pacific Partnership. The focus is intentionally on the treaties, with previous decisions used to illustrate possible interpretations without being elevated to a source of international law. Before analysing the protections afforded by investment treaties, the issues and foreign investment scenarios are outlined in Chapter 2. This illustrates where the disclosure, use or regulation of a trade secret may displease a foreign investor and considers the foreign investor’s relation to the trade secret. For the foreign investor to have a viable claim, their trade secret needs to amount to an ‘investment’, the meaning of which is discussed in Chapter 3. Assuming there is an investment, two substantive protections are considered, expropriation in Chapter 4 and fair and equitable treatment in Chapter 5. A valid exercise of police powers can mean no compensation is owed for what otherwise appears to be an expropriation. I consider police powers in Chapter 6 with a focus on the legitimate public welfare objectives forming the basis for a valid exercise of police powers. Chapter 7 concludes, suggesting where the disclosure, use or regulation of a trade secret may amount to an expropriation for which compensation is owed or conduct inconsistent with fair and equitable treatment.