Work Breakdown Structure (WBS) is a deliverable-oriented hierarchical decomposition of project scope into manageable components. Developed as a core project management tool in the 1960s for defense and aerospace projects, WBS remains fundamental to modern project planning across industries. It transforms abstract project goals into concrete work packages by systematically breaking down deliverables through multiple levels, creating a visual roadmap that ensures nothing is overlooked. The key insight: a properly constructed WBS focuses on what will be delivered (nouns), not how work will be performed (verbs), which distinguishes it from schedules and activity lists and makes it the foundation for accurate estimating, resource allocation, and scope control.