An intermediary (also known as a middleman or go-between) is a third party that offers intermediation services between two parties, which involves conveying messages between principals in a dispute, preventing direct contact and potential escalation of the issue. In law, intermediaries can facilitate communication between a vulnerable witness, defendant and court personnel to acquire valuable evidence, whilst in barter, the intermediary is a person or group who stores valuables in trade until they are needed, parties to the barter or others have space available to take delivery of them and store them, or until other conditions are met.

In diplomacy and international relations, an intermediary may convey messages between principals in a dispute, allowing the avoidance of direct principal-to-principal contact. Where the two parties are geographically distant, the process may be termed shuttle diplomacy. Where parties do not want formal diplomatic relations, an intermediary state may serve as a protecting power facilitating diplomacy without diplomatic recognition.