Chapter 6 closely analyses the operation of investment treaty clauses promising full protection and security. The chapter shows how armed conflict affects both dimensions of this standard significantly. It suggests that the duty to not cause unlawful harm to foreign investors and their invesments should be interpreted as a duty to comply with international humanitarian law standards when applied to the conduct of hostilities. This approach, deriving from the interaction of human rights with humanitarian rules, avoids normative inconsistencies. The due diligence obligation to protect foreign investors and their investments from third-party harm, on the other hand, should be understood as inherently sensitive to prevailing conditions. The state’s (constructed) knowledge of threats to foreign investments, its capacities and resources to counteract these threats, and the notion of reasonableness should guide the analysis under the due diligence standard. The latter element introduces a corrective balancing exercise, opening the way to factor in overriding military or humanitarian concerns.