Class Diagrams
Class diagrams are the backbone of almost every object oriented method, including UML. They describe the static structure of a system.

Object Diagrams
Object diagrams describe the static structure of a system at a particular time. They can be used to test class diagrams for accuracy.

Use Case Diagrams
Use case diagrams model the functionality of system using actors and use cases.

Activity Diagrams
Activity diagrams illustrate the dynamic nature of a system by modeling the flow of control from activity to activity. An activity represents an operation on some class in the system that results in a change in the state of the system. Typically, activity diagrams are used to model workflow or business processes and internal operation.

Sequence Diagrams
Sequence diagrams describe interactions among classes in terms of an exchange of messages over time.

Collaboration Diagrams
Collaboration diagrams represent interactions between objects as a series of sequenced messages. Collaboration diagrams describe both the static structure and the dynamic behavior of a system.

Statechart Diagrams
Statechart diagrams describe the dynamic behavior of a system in response to external stimuli. Statechart diagrams are especially useful in modeling reactive objects whose states are triggered by specific events.

Component Diagrams
Component diagrams describe the organization of physical software components, including source code, run-time (binary) code, and executables.

Deployment Diagrams
Deployment diagrams depict the physical resources in a system, including nodes, components, and connections.