Harmony is the ISS node that connects the Destiny, Columbus, and Kibo laboratories. Also designated Node 2, it functions as a central utility hub for the station’s U.S., European, and Japanese laboratory modules.
Harmony was launched aboard Space Shuttle Discovery on mission STS-120 on October 23, 2007. Astronauts initially attached it temporarily to Unity, then moved it to its permanent position on the forward end of Destiny in November 2007. Columbus later connected to Harmony’s starboard port, while Kibo connects on the port side.
The module has six Common Berthing Mechanism ports. Besides linking laboratories, Harmony distributes electrical power, data, air, and other station resources. It also contains crew quarters and provides berthing locations for visiting cargo spacecraft.
A common mix-up is Unity, which is Node 1 and an earlier central connection point. Tranquility is Node 3, primarily associated with life-support systems, observation facilities, and the station’s cupola—not the three laboratory connections named in the question.