The article argues against the widespread view that OSCE long-term missions should be constrained in their use of public diplomacy. The case rests on arguments that link the emergence of post-international politics to the need for a transformation of diplomatic practices. Missions need to engage in more and better public diplomacy because, in their host countries, subnational actors have the capacity to derail (or advance) the implementation of OSCE standards, even if national governments support (or oppose) mission goals. Diplomats who operate in such an environment cannot confine themselves to mission-to-government communication in their attempts to promote international security through domestic reforms. To illustrate the argument that missions have to reach out to local audiences in order to be effective agents of domestic change, a case study of the mission to Croatia is presented. Shortcomings in the mission’s approach are pointed out, and it is argued that recent improvements in the implementation of OSCE standards are related to changes in the mission’s diplomatic practices. In the conclusion, the article identifies steps the OSCE can take to enable and encourage missions to pursue more and better public diplomacy.