The rise of social media has led to unprecedented opportunities for individuals to share, or express, their attitudes on social and political issues. What factors affect whether individuals choose to share? This research identifies a novel determinant of attitude sharing—support-oppose framing, defined as whether individuals think of their own attitude in terms of what they support or what they oppose. Support-oppose 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). Seven experiments, two correlational studies, and one field study provide evidence for a support-oppose 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, which facilitates greater attitude sharing. In the second, support-framed attitudes are believed to promote more positive impressions, which also leads to greater sharing. This effect is attenuated when individuals’ typical impression-management goals are relaxed.