Rolling Wave Planning is a technique that enables you to plan for a project as it unfolds. This technique, then, requires you to plan iteratively. The planning technique is very similar to those used in SCRUM or other Agile Methodologies. Essentially, when you use Rolling Wave Planning, plan until you have visibility, implement, and then re-plan.
For example, suppose you expect to complete the project in eight months, but only have clarity for the first three months: You would plan only for those three months. As the project progresses and you gain more clarity, you would then plan for the remaining months. The Rolling Wave Planning technique uses progressive elaboration, which is the act of elaborating the work packages in greater detail as the project unfolds.
This method for planning does not exempt you from creating a list of milestones and assumptions for the entire project. As a matter of fact, it is necessary to provide key milestones and assumptions as they will help stakeholders see why you are using Rolling Wave Planning and what to expect as the project progresses.
PMP Exam: Rolling Wave Planning and Progressive Elaboration are concepts that are often quizzed in the PMP exam.