Bill of Materials is a comprehensive list of all the materials and parts that a contractor needs to make a particular product. The BOM should include not only raw materials but also any assemblies, sub-components, and parts, as well as the exact quantity of each of them. The exact layout of the BOM will vary depending on the nature of the work being developed, but there are generally two different types of BOMs for each product: -An engineering phase for developing the product, and -Another mass production stage for delivering products to customers.