技术创新是推动经济发展和社会进步的主要动力，而研发（R＆D）创新是技术创新的关键环节。对于企业而言，研发创新是企业竞争战略的重要组成部分，能够改善企业的市场经营条件，使得企业拥有市场权力、获得垄断利润。产品具有网络外部性是指消费者使用该产品获得的效用随着使用该产品或者兼容产品的其他消费者数目增多而增加。具有网络外部性的行业通常为一些高新技术行业，例如，计算机软件、硬件产品，通信产品，消费类电子产品等。在这些行业中企业研发创新更加活跃、竞争更加激烈、产品更新换代更加频繁。因此，研究存在网络外部性的行业中竞争企业的研发创新策略是一项非常重要的课题。基于此，本书运用博弈理论对网络外部性市场中企业研发竞争策略进行了研究。具体包括如下几个方面：1.基于水平差异化博弈模型的不确定研发模型。这部分产品创新的目的在于增加产品的保留价格。企业研发时对研发结果通常是不确定的，这部分通过拓展Hotelling模型对不确定R＆D进行了研究。在市场完全覆盖的情形下，探讨了双寡头企业的研发竞争策略。研究发现：当两产品边际成本相同时均衡研发成果只受溢出和研发成本参数影响，当两产品边际成本不同时均衡研发成果还会受到网络外部性和产品兼容性的影响；当产品不完全兼容时，网络外部性的出现使得企业更有动机选择风险较大的研发项目；社会最优时行业内总研发成果高于竞争时的情形；企业的工序创新和增加保留价格型产品创新存在互补关系，并且网络外部性能够增强这两类创新的互补程度。2.基于代表性消费者模型的不确定研发模型。由于市场并不总是完全覆盖的，这部分假定市场部分覆盖，通过拓展代表性消费者模型研究研发存在不确定性时企业研发竞争策略。研究发现：在两企业产品的边际成本相同和不同两种情形下，均衡研发策略受网络外部性、溢出效应以及兼容性的影响可能不同；社会最优时总研发成果可能高于也可能低于均衡时行业总研发成果；当产品兼容性充分小时，网络强度越大市场越有可能表现出过度投资；当研发不存在溢出时，企业的工序创新和增加保留价格型产品创新是互补关系，并且网络外部性能够增强这两类创新的互补程度。3.水平产品创新博弈模型。通常把增加产品差异化为目的的产品创新称为水平产品创新，这部分研究了双寡头企业进行水平产品创新竞争时研发策略问题。研究发现：网络外部性的出现使得低边际成本企业均衡产品创新成果高于高边际成本企业成为可能；当产品边际成本相同时两企业均衡产品创新成果均随着网络强度和兼容度增加而增加，当产品边际成本不同时可能出现低边际成本企业均衡产品创新成果随着网络强度增加而减少的情形；社会最优时总产品创新成果高于企业竞争的情形；企业的工序创新抑制水平产品创新的进行，水平产品创新促进还是抑制工序创新依赖于网络外部性、兼容性、总产品创新水平。4.基于纵向差异化模型的工序和产品创新模型。有时企业进行产品创新的目的在于提高其产品质量，这类研发创新也称为垂直产品创新。这部分假定企业质量存在差异，研究企业同时考虑工序和产品创新时的研发竞争策略问题。研究表明：在市场覆盖的程度、不同类型研发创新的顺序、产品创新成本的形式不同时，双寡头企业的研发策略以及网络外部性对研发策略的影响可能不同。 关键词：R＆D　网络外部性　产品创新　工序创新　博弈论　溢出效应 兼容性

Technology innovation is the main driving force to promote economic development and social progress，while R＆D innovation is the key link of technology innovation.For firm，R＆D innovation is an important component of competitive strategy，which can improve the operating conditions of the market，have market power and access to monopoly profits.The network externality in an industry is that the benefit that consumers enjoy from purchasing one or several of its goods depends on the number of other consumers that use the same or compatible goods.The industries exhibiting network externality are usually some high -tech industries，such as the computer industries，the telecommunication industries，the consumer electronic industries，and so on.In these industries，R＆D innovation is more active and product updates more frequently than industries without network externality.Therefore，to study the R＆D innovation strategy of competitive firms is a very important issue in industries with network externality.Based on this，the book uses game theory to research R＆D competitive strategies in the market with network externality.1.The game model of R＆D innovation under uncertainty based on horizontally differentiated model.In this part，product innovation is aimed at increasing reservation price.As we all know，the final outcome is generally uncertain when firm implements a R＆D project.Assumed R＆D innovation under uncertainty and the market fully covered，this part investigates duopoly firms’R＆D competitive strategies by a variant Hotelling model.The main findings are as follows.First，when two firms’marginal costs are equal，the equilibrium R＆D efforts are only depend on the spillover and R＆D cost parameters，but when two firms’marginalcostsdiffer，theyarealsoaffectedbynetworkexternalityand compatibility.Second，when firms’products are partially compatible，the probability that expected profit increases with R＆D risk will increase with network intensity.Third，the aggregate equilibrium R＆D level is smaller than the social optimum.Finally，firm’s process innovation and its product innovation aimed at increasing reservation price complements.Moreover，the intensity of complementarity between R＆D innovations increases with network intensity.2.The game model of R＆D innovation under uncertainty based on representative consumer model.As we all know，the market is not always fully covered.Though assuming the market partially covered，this model studies firm’s R＆D competitive strategies by a variant representative consumer model.The main conclusions are as follows.First，when the marginal costs are same，firms’equilibrium R＆D efforts affected by network externality（or spillover effect and compatibility）are same.But when the marginal costs differ，firms’equilibrium R＆D efforts affected by network intensity（or spillover effect and compatibility）may differ.Second，aggregate equilibrium R＆D level may be bigger（or smaller）than social optimum.Third，when compatibility is small enough，the probability that firms invest too much than social optimum increases with network intensity.Finally，when not consider R＆D spillover，firm’s process innovation and its product innovation aimed at increasing reservation price are complements and the intensity of complementarity between R＆D innovations increases with network intensity.3.The game model of horizontal product innovation.When a R＆D innovation is aimed at increasing the degree of differentiation among goods，we call it horizontal product innovation.This part investigates the R＆D competitive strategies when duopoly firms implement horizontal product innovation.The main results are as follows.First，the firm with low marginal cost investing more than the one with high marginal cost may happen only when the market exhibits network externality.Second，equilibrium product innovation efforts increase with network strength or compatibility when firms’marginal costs are equal，but equilibrium product innovation effort of the firm with low marginal cost may decrease with network intensity when firms’marginal costs differ.Third，aggregate equilibrium productinnovation effortis smaller than social optimum.Finally，both firms’process innovation can reduce their horizontal product innovation，but horizontal product innovation improving or reducing their process innovation depends on network externality，compatibility and aggregate efforts of product innovation.4.The game model of process and product innovation based on vertically differentiated model.In this part，product innovation is aimed at improving product quality（or call vertical product innovation）.We research the R＆D competitive strategies when two firms’qualities differ and each firm carries both process innovation and vertical product innovation.The studies show that the R＆D competitive strategies and how network externality affects R＆D decisions depend on the cover degree of market，the sequence of different innovations and the form of product innovation cost. Keywords：R＆D；network externality；product innovation；process innovation；game theory；spillover effect；compatibility