Is happiness contagious online? To answer this question, this paper investigates the posting behavior of users on Twitter.com, a popular online service for sharing short messages. Specifically, we use automated sentiment analysis to study a large sample of over 46,000 Twitter messages that reference the 2010 Winter Olympics. We determined that there are more positive messages than negative, and that positive messages are more likely to be forwarded than negative messages. However, we were not able to confirm with a reliable degree of certainty that the emotional context of messages is directly related to the user's position in the Twitter network. It is likely that there are other factors involved as well. For example, we found that negative users were more prolific posters than positive users, suggesting their more argumentative and passionate nature. This paper concludes with some implications for the Twitter community and a description of our follow-up study.