The PID is the contract
The project initiation documentation is the baseline against which the project is managed and assessed. It gathers what the project is, why, how it will be delivered, by whom, and the controls — and it is baselined at initiation and only changed under formal control.
Why it is like this
The board needs one artefact that represents the agreement it authorised, otherwise there is nothing to assess the project's end state against.
Not to be confused with
A single document, or a static one. It is a collection of management products, it may be assembled from existing ones, and it is updated at each stage boundary — with the original version preserved so the project can be assessed against what was agreed.
In practice
If the PID is rewritten in place at each boundary, the end project report has nothing to compare against. Keeping the initial baseline is the point.
Source: Managing Successful Projects with PRINCE2, 7th edition (PeopleCert, 2023) — PRINCE2 7, Appendix A — project initiation documentation. Read on .
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Predict Check yourself
At each stage boundary the team updates the PID in place, overwriting it. What is lost?
Show the answer
The original baseline — the end project report needs it to assess the project against what was originally agreed.
The PID evolves, and the version authorised at initiation is kept. That pair is what makes the closing assessment meaningful.