This study examines political opinion expression on four social media platforms in Argentina (Facebook, Instagram, Twitter and WhatsApp). Drawing on in-depth interviews (N=158) and a survey (N= 700), it examines divergent dynamics of political conversation across platforms, and finds that respondents use platforms in different ways to talk about current affairs. Political discussion practices vary according to shared understandings regarding the content perceived as appropriate and level of privacy attributed to each platform, but not according to socio demographic characteristics. This comparative cross-platform approach indicates that political talk on social media is shaped by: a) the political context; b) each platform’s uptake; and, c) the overlapping of private and public, non-political and political content in a single space. Combining interviews with a survey allows this research to account for both differences in the level of political talk across platforms and the interpretation that underlie these differences. In the polarized Argentine context, online incivility is perceived to be common, and users employ diverging strategies to talk about politics on different platforms. We draw upon these findings to reflect on how varying user practices contribute to understanding social media platforms as culturally distinct spaces.