Publisher Summary The chapter analyzes and compares the investment incentives of platform and application developers for Linux and Windows. It finds that the level of investment in applications is larger when the operating system is open source rather than proprietary. The comparison of the levels of investment in the operating systems depends on reputation effects and the number of developers. It also develops a short case study comparing Windows and Linux and identifying new directions for open source software research. The chapter analyzes the incentives to invest in application software and an operating system under two different software ecosystems: one based on an open source operating system, such as Linux, and the other based on a proprietary operating system, such as Microsoft Windows.