The rise of social media has led to unprecedented levels of sharing, on topics ranging from what products people like to their views on polarized issues and policies. What factors affect whether individuals choose to share their attitudes? In this paper, we identify a novel determinant of whether individuals share—attitude framing, defined as whether individuals think of their own attitude in terms of what they support or what they oppose. Attitude framing is distinct from attitude valence, as the same attitude can be framed in terms of support (e.g., I support that this policy is bad) or opposition (e.g., I oppose that this policy is good). Five experiments and one field study provide evidence for an attitude-framing effect, whereby individuals are more likely to share, or express, attitudes framed in terms of positions they support rather than positions they oppose. This effect occurs via two pathways. In the first, support-framed attitudes are viewed as more value expressive, and thus lead to greater sharing. In the second, support-framed attitudes are believed to foster more positive impressions from message recipients, which also leads to greater sharing. This attitude-framing effect is attenuated when individuals do not want to be liked by the target of their sharing.