Project Management Processes
When managing a project you have to take many steps to go from the beginning to the end of the project. Some examples of these steps are "Develop Project Management Plan", "Manage Project Team", "Control Schedule" etc. These steps can be seen as processes.
In total there are more than forty Project Management Processes. A complete overview of all the Project Management Processes can be found in chapter 3 of PMI's PMBOK.
These forty something Project Management Processes are grouped into the following five Project Management Process Groups:
Processes in the Initiation, Planning, Execution and Closing Process Groups are performed sequentially as the project progresses from initiation to closing.
Processes in the Controlling Process Group are performed throughout the entire project.
Why is Grouping Important?
Grouping of the Project Management Processes provides for a structured approach to managing your projects. Discipline yourself to stick to sequence of the Process Groups. As an example, when a business case is needed, it should be done during the initiation of a project or do not start talking to contractors before you went through the planning processes. How would you know what to talk about before you have a project plan?