We consider two firms selling products to a market of network-connected customers. Each firm is selling one product and the two products are substitutable. The customers make purchases based on the multinomial logit model and the firms compete for their purchasing probabilities. We characterize possible Nash equilibria for homogeneous network interactions and identical firms: when the network effects are weak, there is a symmetric equilibrium that the two firms evenly split the market; when the network effects are strong, there exist two asymmetric equilibria additionally, in which one firm dominates the market; interestingly, when the product quality is low and the network effects are neither too weak nor too strong, the resulting market equilibrium is never symmetric although the firms are ex ante symmetric. We extend these results along multiple directions. First, when the products have heterogeneous qualities, the firm selling inferior product can still retain market dominance in equilibrium due to the strong network effects. Second, when the network effects are heterogeneous, customers with higher social influences or larger price sensitivities are more likely to purchase either product in the symmetric equilibrium. Third, when the network consists of two communities, market segmentation may arise. Fourth, we extend to the dynamic game when the network effects build up over time to explain the first-mover advantage.

"The discrete choice approach provides an ideal framework for describing the demands for differentiated products and can be used for studying most product differentiation models in the literature. By introducing extra dimensions of product heterogeneity, the framework also provides richer models of firm location and product selection."--BOOK JACKET.

In this paper we study a duopoly where the network effect is nonmonotone and the network can be overloaded. The firms choose prices and locations endogenously, and the agent's utility is influenced by the number of people patronizing the same firm she does. We determine the market equilibrium, and we study how the network effect influences social welfare. We compare this setting with the standard horizontal differentiation model with no network effects to understand whether and how conformism is socially desirable. The results show that whether network effects are desirable depends on how people are conformist, and whether overloading is feasible. If overloading is not possible (in either of the firm's network), and the total consumers' mass is sufficiently high, a network effect which is slightly concave increases social welfare. By contrast, if overloading is feasible, and the total consumers' mass is sufficiently small, social welfare is increased if the network effect is more concave than in the previous case.

In this paper, we formulate a differential game model to investigate firms' competition in both price and product R&D. The significant features of our research include: (i) incorporating the factor of network effects into the framework of continuous dynamic competition; (ii) considering the consumers' adaptive learning about the network size in the spirit of behavioral economics. Our analysis mainly suggests: (i) The network effects and consumers' adaptive learning comprehensively have negative effects on the result of price competition but has nothing to do with the result of R&D competition under duopoly, which is not true as the number of firms increases; (ii) the incentive to acquire competitors' state information is increasing with the intensity of network effects and the consumers' learning speed; (iii) when we consider the competition among more than three firms under feedback information structure, the competition intensity has negative effect on the steady-state quality stock; (iv) in a market where the consumers show strong price sensitivity, the product quality is under-provided compared with the first-best optimal level regardless of the choice of solution concept.

Determinants of firm and market organization; Analysis of market behavior; Empirical methods and results; International issues and comparision; government intervention in the Marketplace.