Electronic copy available at: http://ssrn.com/abstract=1177443 Electronic copy available at: http://ssrn.com/abstract=1177443 Electronic copy available at: http://ssrn.com/abstract=1177443 MANAGEMENT SCIENCE Vol. 51, No. 10, October 2005, pp. 1494–1504 issn 0025-1909  eissn 1526-5501  05  5110  1494 inf orms ® doi 10.1287/mnsc.1050.0400 ©2005 INFORMS Two-Sided Network Effects: A Theory of Information Product Design Geoffrey G. Parker Tulane University, New Orleans, Louisiana 70118, gparker@tulane.edu Marshall W. Van Alstyne Boston University, and Massachusetts Institute of Technology, Boston, Massachusetts 02215, mva@bu.edu H ow can firms profitably give away free products? This paper provides a novel answer and articulates trade-offs in a space of information product design. We introduce a formal model of two-sided network externalities based in textbook economics—a mix of Katz and Shapiro network effects, price discrimination, and product differentiation. Externality-based complements, however, exploit a different mechanism than either tying or lock-in even as they help to explain many recent strategies such as those of firms selling operating systems, Internet browsers, games, music, and video. The model presented here argues for three simple but useful results. First, even in the absence of competition, a firm can rationally invest in a product it intends to give away into perpetuity. Second, we identify distinct markets for content providers and end consumers and show that either can be a candidate for a free good. Third, product coupling across markets can increase consumer welfare even as it increases firm profits. The model also generates testable hypotheses on the size and direction of network effects while offering insights to regulators seeking to apply antitrust law to network markets. Key words : network effects; network externalities; two-sided markets; free information; business models; strategic complements; product design History : Accepted by Rajiv D. Banker, information systems; received April 29, 2003. This paper was with the authors 5 months for 2 revisions. 1. Introduction This paper seeks to explain strategic pricing behav- ior and product design decisions in network markets. Given the seemingly anomalous practice of free- pricing, how is it possible that firms are willing to subsidize information and related products, appar- ently expecting neither future consumer exploitation nor tying? Why do firms give away applications development toolkits, portable document readers, and Internet browsers without metering tie-ins to those same consumers? What theory explains this economic logic? In answer, we find that designing matched prod- uct pairs and discounting one relative to the inde- pendent goods case changes the shape of demand in markets joined by network effects. The insight is that characterizing network markets may require not only product standardization, essential to demand economiesofscale(KatzandShapiro1985,Farrelland Saloner 1986), it may also require recognizing sharp distinctions between consumer types. This is essential for managing demand interdependence, implement- ing price discrimination, and raising barriers to entry. Contributing to the recent two-sided network exter- nality literature, we introduce a novel mechanism (i) that explains firms’ unbundled component sales and pricing strategies, (ii) that shows which half of a two-sided network market to discount, (iii) that is dis- tinct from tying and traditional multimarket price dis- crimination, and (iv) whose formulation is robust in results to multiple specifications of demand. Of man- agerial interest is the proposition that discounting an unbundled component can increase profits to the point where negative prices become optimal. This helps not only the monopolist but also the oligopoly firm seeking barriers to entry. Profits increase con- ditionally, however, on promoting network effects through clever product design. They depend also on the correct choice of market to discount. Of legal and economic interest is the implied industry concentra- tion and difficulty applying antitrust tests of preda- tion. Pricing below marginal cost maximizes profits even in the absence of competition. Platform interme- diaries that internalize these externalities can improve consumer welfare as well as profit. The paper proceeds as follows. Section 2 provides a review of related literature in network externalities, multiproduct pricing, and bundling. In §3, we first develop a model of externality-based complements. We find the conditions for a subsidy market to exist 1494