In project management, a Work Breakdown Structure (WBS) is an exhaustive, hierarchical (from general to specific) tree structure of deliverables and tasks that need to be performed to complete a project. The Work Breakdown Structure is a very common and critical project management tool. It is considered such a key part of project management that many United States government statements of work require a WBS. The purpose of a WBS is to document the scope of a project. Its hierarchical arrangement allows for easy identification of the terminal elements (the actual items to be done in a project). Being an exhaustive document of the project scope, the WBS serves as the basis (indeed, the backbone) for much of project planning. All the work to be done in a project must trace its origin from one or more WBS entries.

How to build a WBS

WBS is simply an organized presentation of the work required to complete the project. There is any number of ways to organize the presentation of the work. For example, one could organize it according to life-cycle phases, showing each phase as a top-level breakdown. Another way to organize it is by functional responsibilities. A key thing to remember is that the WBS documents the scope of the project, and not the execution plan of the project. Thus, in the house painting example below, 'Prepare Materials' could appear after 'Paint the Room' and it is still a valid and correct WBS. For more details on the various approaches to building the WBS for a project (see e.g. How to Build a Work Breakdown Structure below). Whether the WBS should be activity-oriented or deliverable-oriented is a subject of much discussion. Even suggesting picking one style and then sticking to it can be a point of argument.

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