A subcontractor is a person or business which undertakes to perform part or all of the obligations of another's contract, and a subcontract is a contract which assigns part of an existing contract to a subcontractor.
A general contractor, prime contractor or main contractor may hire subcontractors to perform specific tasks as part of an overall project to reduce costs or to mitigate project risks. In employing subcontractors, the general contractor hopes to receive the same or better service than the general contractor could have provided by itself, at lower overall risk.