Much of the recent research on user contributions to electronic networks has focused on attracting and motivating participations. We, instead, investigate online community defections, their cause, and their impact through an empirical investigation of defections from Wikipedia. Our research uses justice theory to determine the effects of injustice perceptions on contributor defections and draws on fairness heuristic theory to distinguish the relative effects of distributive injustice and procedural injustice. The results show that perceptions of injustice concerning collaboration outcomes ("distributive injustice") raise contributor dissatisfaction, which in turn leads to defection. Perceptions of injustice concerning the process ("procedural injustice"), by comparison, have a direct impact on defections and exert a stronger influence on dissatisfaction than distributive injustice. Justice emerges as a hygiene factor adding to the level of dissatisfaction among dissatisfied contributors but not among satisfied contributors. The findings contribute to our understanding of collaborative knowledge creation by drawing attention to contributors' post hoc passive emotions and behaviors instead of predominantly investigating their initial prosharing behaviors. The work also has practical implications for community governance because it suggests how to sustain communities in the long term.