Work breakdown structure describes a method for representing and organizing the work that will be necessary to accomplish some goal. Creating a work breakdown structure involves taking a complex task with many parts and describing each individually in a single chart. The goal of creating one of these charts is to create clarity about what needs to be done, from the beginning to the end of a project.
A work breakdown structure is usually organized hierarchically. At the top is the main goal: for example, "cook s'mores on a campfire." The goal will then be subdivided into smaller objectives, such as procuring supplies, starting the fire, maintaining the fire, and actually cooking the s'mores. Each of these smaller units can in turn be divided. For example, "procuring supplies" would be divided into shopping for food, gathering sticks, and chopping firewood. Specific tasks may be allocated to different members of the team of people trying to cook the s'mores.
One common feature of work breakdown structures is the 100% rule. The work breakdown structure should contain 100% of the work that needs to be done. It should represent a complete accounting of all tasks that are necessary. It should also not include work that is not necessary for achieving the primary goal. Of course, in the real world, it may be impossible to achieve this perfectly.
Another principle of the work breakdown structure is mutual exclusivity. That is, different elements enumerated on the chart should not overlap with each other. The goal is complete clarity in representing discrete tasks. Keeping the tasks separate is helpful especially in large projects with many participants trying to collaborate without duplication.
A common but optional element of the work breakdown structure is a dictionary. The dictionary is also especially helpful for big projects. The dictionary defines terms and acronyms used in the chart. Providing this type of supplemental explanation increases the likelihood that everyone who sees the document understands it in the same way. Different understandings of the same text can produce just as much confusion as a document that is unclear on its own.
The idea of the work breakdown structure was produced in the Department of Defense during the 50s and 60s. A precursor to the work breakdown structure was used in the creation of Polaris missiles. Eventually, the system became codified in the government document MIL-STD-881, "Work Breakdown Structures for Defense Material Items." The process remains in use by the military, but has also expanded into the corporate world.