Documentation Means Everything
After the project manager and the customer are in agreement about what the project will create, the project manager should create a scope statement, which is a document that captures everything that is considered in scope and defines the relevant things that are out of scope. For example, a project to push an application to 1,500 workstations might define the application, define the overview of the project work, and emphasize that the rollout doesn't include visiting every machine to confirm the existence of the push. The scope statement clarifies the project and requires the project manager, the project sponsor, and sometimes the key stakeholders to sign off on the document.
The scope statement serves as the guide for all future project decisions. The following figure shows the timeline of the project and the relevant influence of the project manager and the stakeholders. Early in the project the stakeholders should have a bunch of influencetheir input is essential. As the project progresses toward completion, notice that the stakeholders' influence wanes as the project manager's influence increases. The intersection of the two paths represents the creation of the scope statement.
In other words, once the scope statement has been agreed upon, the project manager owns the project and works to protect and deliver on the promises established in the scope statement.