The Book of the Plan
The Book of the Plan Answers Three Vital Questions
Whether you call it a Project Master Plan, Project Initiation Document, or anything else, you need a comprehensive document (or, for a large project, a suite of documents) that covers everything: What you are going to do, why you are going to do it, and how you will deliver it.
You will get more detail on the How, in the next lecture.
For this lecture, you may want to download the worksheet I've also added a project planning poster that I prepared to support the launch of my book, How to Manage a Great Project.