Contributors’ withdrawal from online communities is threatening the sustainability of those communities, especially those that have entered mature and saturated stages. Drawing upon organizational withdrawal research, this article re-conceptualizes contributor withdrawal in the context of online communities. To explain the underlying mechanisms by which contributors withdraw from online communities, we introduce a theory of contributor withdrawal that emphasizes within-individual variances on the changes of cognition, emotions, and behaviors, rather than across-individual variances on the final (or average) states. In light of affective events theory, contributors’ cognitive dissonances between the community they experience and the community they expected are identified as distal causes of contributor withdrawal through the mediation of emotional changes. We also propose a typology of cognitive dissonances towards online communities and the structure of emotional change. We then discuss the moderating impacts of affective dispositions and sense-making on the cognitive dissonance-emotional change relationship, and the mediating impacts of changes in attitude and expectation on emotional change-withdrawal behavior relationships.