A traditional view in legal scholarship holds that the U.S. Constitution assigns the president exclusive power to carry on official diplomatic communications with foreign governments. But in fact, Congress and its members routinely engage in communications of their own. Congress, for example, receives heads of state and maintains official contacts with foreign parliaments. And individual members of the House and Senate frequently travel overseas on congressional delegations (“CODELs”) to confer with foreign leaders, investigate problems that arise, promote the interests of the United States and constituents, and even represent the president. Moreover, many of these activities have occurred ever since the Founding. Together, they comprise an understudied field of legislative diplomacy. This Article has two purposes: The first is to use State Department cables from WikiLeaks, a recent compilation of public reports, and original historical sources to provide a uniquely detailed, descriptive account of legislative diplomacy. The second is to develop theories about the practice’s constitutionality. Text, original meaning, and customary practice suggest that the separation of diplomacy powers is more complicated than commonly assumed and that those powers do not belong exclusively to the president. The analysis undermines the “sole organ” metaphor, serves as a counterpoint to the widely held view that authority over foreign affairs belongs overwhelmingly to the executive, and carries practical implications for the execution of U.S. foreign relations.