This chapter presents some facts about multiplanet systems. By mid-2008, 30 extra-solar systems with 2 or more planets had been identified. Their orbits are shown in Tables 1 and 2. The orbits given in these tables were selected from those published as being the most reliable for dynamical studies. Some additional multiplanet systems have been announced in meetings or otherwise, but are not included in the tables since a document on their orbits is not yet available. Table 2 also shows, for comparison, the two subsystems forming the solar system.