The concept of habit has been receiving a lot of attention among Information Systems (IS) researchers. In recent years, we have witnessed a considerable progress in the conceptualization and operationalization of IS habit. However, little theoretical and empirical attention has been given to the formation of IS habit. To fill this gap, this paper builds and tests a theoretical model investigating the factors affecting the formation of habit in the context of Twitter. An online survey was conducted and data from 167 respondents were analyzed using PLS. The results showed that satisfaction, frequency of past behaviour, and convenience were important in determining habitual use of Twitter. In addition, social presence had significant impact on user satisfaction with Twitter. This paper concludes with a discussion of theoretical and practical implications.