The Cassini mission is a joint venture between NASA, European Space Agency (ESA), and Agenzia Spaziale Italiana (ASI). A major interface is between the NASA/Jet Propulsion Laboratory (JPL) provided Orbiter and the ESA provided Atmospheric Probe. The Orbiter is designed to orbit the planet Saturn, while the Probe will descend into the atmosphere and impact the surface of Titan. After years of study and scientific meetings between NASA, JPL, and ESA, a Memorandum of Understanding was signed between NASA and ESA on 17 December 1990. Project teams were formed at JPL and ESA and work began on the interface definition and integration of the Probe onto the Orbiter. Unique challenges were presented due to the fact that this was the first such atmospheric probe designed and developed in Europe, the complicated mechanical and electrical interface between the Probe and the Orbiter, and the nine hour time difference between JPL and ESA. As with the Galileo mission to Jupiter, the Orbiter provides an environmentally acceptable vehicle for the Probe during the long cruise phase, a communication link to Earth for periodic Probe checkouts during this cruise phase, a stable and accurately pointed platform for Probe separation, and a relay link to Earth for the actual Probe mission descent into the Titan atmosphere. Management and technical interchange tools were developed to address these challenges. The Probe design and its interface with the Orbiter are the result of this effort.