This dissertation studies the behavioral characteristics of participants engaged in information exchange in the context of online communities. Online communities are defined as collectives of individuals that use computer mediated communication to facilitate interaction over a shared purpose and/or objective. It is argued that this interaction creates externalities, for example, in the form of codified information that others can use through web search tools. These externalities assemble a virtual form of social capital, a commonly shared resource. The research objective of this thesis is to examine how the behavioral tendencies of the participants in online communities are affected by the way this common resource is formatted, administered and shared. The dissertation consists of two parts: a theoretical part where the empirical background and the object of research inquiry is highlighted, and an empirical part which consists of four empirical studies carried out in the context of three online communities, namely, Google Answers, Yahoo!Answers and Amazon Online Reviews. The empirical part of this dissertation starts with a controlled experiment emulating a well known social dilemma: the public goods game. It provides substance as to whether and when participants in online communities behave (un) cooperatively. The next two studies focus on a special case of online communities where participants ask questions and other participants post answers conditionally on social and monetary incentives. The results of these two studies confirm that community participants do care about the contributions of others and engage in incentive compatible behavior. Yahoo!Answers participants exercise effort in the community by posting answers to questions conditionally on benefits provided by other participants. The empirical findings show that contributing participants in an online community receive answers faster, while those that do not contribute much effort are sanctioned in the form of longer response-time to their questions. In Google Answers this thesis, interactions can be observed that are based on monetary rewards (rather than social rewards in the form of a reputation index as in Yahoo Answers). Participants make use of voluntarily awarded payoffs (tips) along with stated rewards, in order to motivate those that provide answers (answerers) to provide better quality in their responses. The findings of this study confirm the symmetric effect between monetary rewards and quality. However, this study also identifies cases where social norms have a significant effect on response behavior. When participants seek to get better service with less effort (in terms of total cost), a reputation index which is constructed by the history of their previous interactions supports such an attempt. In other words, reputation history influences information sharing behavior in online communities. The last chapter of the empirical part focuses on another crucial aspect of information as a shared resource: Clarity and understandability. The study examines online product reviews on Amazon.com. The results suggest that participants do care about the clarity of this codified form of experience which increases a helpfulness index accordingly. The thesis overall finds symmetric effects between participation in online communities and output of interaction, but also identifies the ability of the participants to interact strategically as they seek to minimize the effort they provide in order to find the information they seek. The results underline the importance of signaling and quality evaluation mechanisms as counter-balancing control that can enhance activity on online communities
