State Diagrams are an aspect of UML that describe the behavior of one object over several use cases in the system. A state describes the condition of an object at a given point in its lifetime. A state diagram describes all possible states of an object, and the paths to get from one state to another when an external event is received.

A state is represented by a rounded rectangle that contains the state name. There are two special states, the start state and the final state. The start state is represented by a solid circle, and shows where the initial work of the object is done. A final state is reached when the object's lifetime is over. A final state is represented by a solid circle surrounded by an open circle.

States are connected together by transitions that point from a source state to a destination state. The behavior that causes the state change, such as an event, conditions, or time, if there is any, is described near the arrow. A transition with no events, conditions, or time limits, is performed automatically upon completion of the state's activities.