As per PMBOK 5th Edition there are total of 5 process groups.
1. Initiating- Develop project Charter and Identify stake holder are 2 processes in this group. This group manages the process which are performed during a project or Phase start ups.
2.Planning- Planning is one of the major group. This is the one group where all knowledge area has at least one process. There are total 24 processes.Planning process group is responsible for creating project management Plan, Scope base lines, Schedule Base lines different project documents etc.
3.Executing- This is the group where actual project work occurs. There are 8 different processes in this group.
4.Monitoring and Controlling - This is the group where project activities are monitored and approvals are taken for a change request. There are total of 11 processes.
5. Closing.- Here is formal closer of project or Phase, and it contains 2 processes.
Important thing to remember here is Process groups also not sequential as listed rather Planning, Monitoring and control and executing is kind of cyclic in nature, In every revision on Change request Plans gets updated and as per the Plan execution takes place and while executing or monitoring change request gets submitted.
So the process is as close as the image below.