Complementors are businesses that directly sell a product (or products) or service (or services) that complement the product or service of another company by adding value to mutual customers; for example, Intel and Microsoft (Pentium processors and Windows), or Microsoft and McAfee (Microsoft Windows & McAfee anti-virus).

Complementors are sometimes called "The Sixth Force" (from Porter's Five Forces model), a term which was coined by Adam Brandenburger.

• Porter's five forces analysis

• Brandenburger and Nalebuff, Architecture Wins, 1998
• Brandenburger and Nalebuff, The Value Chain, 1998
• Nalebuff and Brandenburger, Co-opetition, 1995