Most types of networks, over time, spawn the creation of complementary stocks that enhance network value. Computer operating systems, for example, induce the development of the complementary stock of software applications that increase the value of the operating system. In this paper, we challenge the conventional wisdom that a large network, which induces the creation of large complementary stocks, serves as a barrier to entry that protects the incumbent from competition or network capture. We show that a larger network may either deter or attract entry depending on the relation between the network quality and the cost of an innovator's network product. The probability of entry also depends on the level of compatibility between the potential entrant's technology and existing complementary stocks, which in turn is influenced by the strength of the intellectual-property-rigths environment. Intellectual property rigths and the associated threat of entry may affect and incumbent's choice of network size in counterintuitive ways.
