Social media use has become increasingly popular among police forces. The literature suggests that social media use can increase perceived police legitimacy by enabling transparency and participation. Employing data from a large and representative survey of Dutch citizens (N = 4,492), this article tests whether and how social media use aﬀects perceived legitimacy for a major social media platform, Twitter. A negligible number of citizens engage online with the police, and thus the ﬁ ndings reveal no positive relationship between participation and perceived legitimacy. The article shows that by enhancing transparency, Twitter does increase perceived police legitimacy, albeit to a limited extent. Subsequent analysis of the mechanism shows both an aﬀective and a cognitive path from social media use to legitimacy. Overall, the ﬁndings suggest that establishing a direct channel with citizens and using it to communicate successes does help the police strengthen their legitimacy, but only slightly and for a small group of interested citizens.