To make democracy work, citizens must be empowered to seek and receive information from their governments. To this end, states have infused principles of transparency into national laws and negotiated international (human rights) conventions that promote access to official documents held by public authorities. These legal sources confirm that the public’s right to access and disseminate information is fundamental but not absolute. One of the exceptions to the “open government” system relates to diplomatic information. Diplomatic services and international negotiators can shield documents from disclosure to avoid their release impeding effective negotiations or causing harm to diplomatic partners. Consequentially, diplomats still operate largely outside the scrutiny of the public, with little oversight by parliaments. The present chapter advances the thesis that the diplomatic exception, while very much needed for governments in the exercise of international relations, is not without limits. It therefore seeks to define legally the exception’s scope and to research the practical implications in an ever-evolving environment: diplomatic cables’ have been leaked, citizens’ expectations have risen, and diplomatic services have developed public diplomacy strategies. The chapter determines the rational grounds of legitimation and validation of diplomatic secrecy and tests those against the needs of foreign services as defined under modern standards of openness and transparency.