The universe has provided us with multiplanet systems, laboratories in which we can test the physics of planet formation. I will talk about three ways in which we can use multiplanet systems as laboratories. (1) We can study the orbital dynamics of a single multi-planet system in detail. (2) In each multiplanet system, we can compare a planet to its siblings, developing statistics over many systems. (3) We can compare multiplanet systems to systems with only one known planet. My talk will draw on results from the California Kepler Survey, which provided new stellar and planetary properties for 909 transiting planets in 355 multiplanet systems, as well as well-known individual systems.