An organizational breakdown structure (OBS) is a hierarchical chart that arranges a project’s work by the organisational units responsible for it – departments, teams or roles – rather than by deliverable. It shows who is accountable for which parts of the work.
By mapping work packages to the units that will perform them, an OBS clarifies responsibility and helps roll up cost and progress by organisation. It complements the work breakdown structure, which organises the same work by deliverable.
Related: work breakdown structure, responsibility, RACI.
Last updated: 4 July 2026 · By Tom, PMP-certified since 2004