In this article we argue that trust is fundamental to post-agreement negotiations in the field of international security. We present our concept of interstate trust and discuss its relation to two core mechanisms of international cooperation: control and policy integration. Our main hypothesis is that growing trust reduces a dyad’s reliance on control and leads to intensified policy integration. To specify how the trust-control nexus and the trust-integration nexus structure post-agreement negotiations, we first assume that post-agreement negotiations are likely to follow interstate crises. Second, we theorize crisis reactions and differentiate between low-trust and high-trust situations. In low-trust situations, a crisis indicates a failure to control the actions of others. As a response, demands for institutional reform will stress new and improved control mechanisms. In high-trust situations, the trusting bias defuses most of the doubts about the other’s cooperative preferences and points to miscommunication as the principal issue. Therefore, negotiations will be about intensifying policy integration. States do so for three purposes: sustaining valuable integration, overcoming the crisis, and building trust. As a first plausibility probe for our argument, we look at post-agreement negotiations between France and Germany.