Results from classical dynamical systems are generalized to hybrid dynamical systems. The concept of limit set is introduced for hybrid systems and is used to prove new results on invariant sets and stability, where Zeno and non-Zeno hybrid systems can be treated within the same framework. As an example, LaSalle's Invariance Principle is extended to hybrid systems. Zeno hybrid systems are discussed in detail. The limit set of a Zeno execution is characterized for classes of hybrid systems.