WWPMM defines a baseline as the reference data on which execution of project activities are planned and controlled. A baseline consists of elements of the agreement and the project management plans. A baseline might also be considered as the original plan, plus or minus approved changes.
A baseline becomes formal after the involved stakeholders review and approve it, then sign off in writing. After it is established, the baseline is under change control.
Why Establish Baselines?
Changes occur in almost every project. Experience has shown that without baselines, managing change is very difficult, if not impossible. Unmanaged change can cause the scope to increase to the point where the project is out of control.
Establishing a baseline helps you determine boundaries for the project, including what is being developed, when it is scheduled to be delivered, and how much it is projected to cost.