A Bill of Materials (BOM) is the foundational data structure in manufacturing. It defines what goes into a product — every part, material, fastener, and consumable — along with the quantity required for each. BOMs can be flat (single level) or indented (multi-level), reflecting the hierarchy of assemblies and sub-assemblies.
BOMs drive procurement, production planning, costing, and inventory management. An inaccurate BOM cascades errors through every downstream process: wrong materials get ordered, production stops for missing parts, and costs deviate from estimates.
In engineer-to-order and configure-to-order environments, BOMs are often dynamic — they change with each order based on customer specifications. Managing BOM revisions, effectivity dates, and approved substitutions is a core challenge that manufacturing software must address.