Saint John's Tower, Medieval tower in Vatican City.

Saint John's Tower is a round medieval structure on the westernmost hilltop of Vatican City, near Vatican Radio and above the Vatican Gardens. It stands along the wall built by Pope Nicholas III and was rebuilt by Pope John XXIII in the early 1960s. It now houses the Secretariat for the Economy.

The building was constructed as part of a defensive wall under Pope Nicholas III. After falling into decay during the early 1500s, it was rebuilt and restored under Pope John XXIII.

The tower's name comes from John, and its rooms have served as a residence for guests of the popes rather than as an office. In 1971 Pope Paul VI let Cardinal József Mindszenty stay here after the Hungarian prelate left the U.S. embassy in Budapest, where he had lived in asylum. In 2006 Cardinal Tarcisio Bertone moved in after becoming Secretary of State, while Cardinal Angelo Sodano stayed in the official residence.

The tower stands at the westernmost tip of Vatican City, near Vatican Radio and above the Vatican Gardens, inside areas closed to the public. It can be seen from paths through the gardens when they are open by permit, or from outside the Vatican walls on the Rome side.

In 2008, the tower served as an unusual venue for a high-level diplomatic meeting when a major world leader was received here instead of at the customary location. This choice highlights how the building plays a varied role in Vatican diplomacy.