Open innovation research and practice recognize the important role of external complementors in value creation. At the same time, firms need to retain exclusive control over some essential components to capture value from their product and/or service system. This paper contributes to the literature by analyzing some of the trade-offs between openness to external value creation and closedness for internal value capture. It focuses on selective openness as a key variable and investigates how it affects value creation by external complementors, specifically the members of user innovation communities. Openness, it is hypothesized, matters to community members: The more open a product design is, the higher their sense of involvement in the innovation project, and the larger the effort they devote to it. Unlike prior literature, different forms and loci of openness are distinguished, specifically the transparency, accessibility, and replicability of different components of the product being developed. Hypotheses are tested based on survey data (n = 309) from 20 online communities in the consumer electronics and information technology hardware industries. Multilevel regression analysis is used to account for clustering, and thus nonindependent data, at the community level. We find that openness indeed increases community members' involvement in the innovation project and their contributions to it. Interestingly, however, some forms and loci of openness strongly affect community perceptions and behavior, while others have limited or no impact. This finding suggests that, at least in relation to user communities, the trade-off that firms face between external value creation and internal value capture is softer than hitherto understood. Contingency factors that may be able to explain these patterns are advanced. For example, users are expected to value the form of openness that they have the capabilities and incentives to exploit. The findings in this paper extend the literature on selective openness in innovation. They emphasize the need to study the demand for different forms of openness at the subsystem level and align supply-side strategies to it. In managerial practice, a careful assessment of the demand for openness enables firms to successfully use selective openness and to effectively appropriate value from selectively open systems.