Empirical evidence indicates that Enterprise Social Networks facilitate intra-organizational knowledge sharing. While organizations continue to invest in Enterprise Social Networks, many implementation projects fail due to insufficient user adoption. Against this background, this paper investigates factors that influence individuals’ adoption of Enterprise Social Networks. We thoroughly reviewed the existing literature and crafted a comprehensive adoption model. Besides commonly known adoption factors, we introduce perceived network externalities and perceived social capital advantage to account for the specific context of Enterprise Social Networks. We tested our model using structural equation modeling and empirical survey data of 155 respondents. Our results show that perceived network externalities are by far the strongest predictor for enterprise social network adoption, followed by perceived enjoyment and perceived social capital advantage. In contrast to other studies, we find perceived usefulness and perceived ease of use to be insignificant.