According to the PMBOK® Guide, the Planning Process Group consists of those processes performed to establish the total scope of the effort, define and refine the objectives, and develop the course of action required to attain those objectives.

A fundamental principle of project management is Progressive Elaboration, which means that as more information or even more accurate estimates become available, the project management plan is updated. Because projects are dynamic, the planning processes are carried out repeatedly throughout the project life cycle.

Rolling Wave Planning: This is a specific form of progressive elaboration where work to be accomplished in the near term is planned in detail, while future work is planned at a higher level.

Feedback Loops: As the project progresses through the Executing and Monitoring and Controlling process groups, changes often require the team to return to the planning processes to update the schedule, budget, or scope (the " Plan-Do-Check-Act " cycle).

Analysis of Distractors:

A. Only once, at the beginning: This describes a " static " plan. In reality, a plan that is never updated is rarely successful, as it does not account for changes or new information.

B. At the beginning and the end: Planning is continuous. While the Closing Process Group occurs at the end, planning is not restricted to these two bookends.

C. Once during each phase: While planning does happen within each phase, it is not restricted to a single event per phase. Within a single phase, planning processes may be revisited many times as the team refines their approach.