During the planning phase of a project, project managers must set expectations and a standard against which all the performance will be measured. In order to do this, project managers establish a baseline, which is a document that describes the project scope, cost and schedule

The project baseline must be documented, agreed upon and approved before the project is executed. Once the project starts, the baseline is used to keep track of the progress and measure performance. 

Project managers should be aware that they must make adjustments to the project baseline in order to achieve success. During project execution, changes to the triple constraints (scope, cost and schedule) can impact the project baseline. Project managers must consider the impacts of these three constraints on the quality of project deliverables.