European youth’s civic engagement and political participation in EU-related issues is a timely imperative. Research findings on youth citizenship range from political apathy to alternative forms of participation, although theoretical evidence remains poor. This study is based on empirical data from the Greek contribution to the European program CATCH-EyoU (Horizon 2020), aiming to explore different forms and predictors of youth’s civic engagement and political participation on EU-related issues. Based on social psychological theoretical background, we assumed that the expressed political interest for the EU translates to specific forms of action. Identification with the EU and perceived political efficacy/alienation were expected to mediate the above relationship. The sample consisted of 749 young adults aged 18-27 (M = 22.2, 50.7% women, 89.7% Greek citizens, 72% university students, 75.5% employed). In addition to voting, four components of political participation and civic engagement were studied, namely conventional participation (in support of political parties and goals), activism (acts of protest against the authorities), online participation (social networks), and volunteering (non-profit actions). Mediation analyses showed that the relationship between political interest and participation can be explained by different mechanisms: The sense of belonging in the EU lead to more frequent electoral participation, but to less activism and online participation. On the contrary, EU identity exploration and reconsideration contributed to increased conventional participation. Political efficacy seemed to promote activism and online participation, while political alienation tended to decrease activism. These findings reveal the multiple connotations of youth’s politicalparticipation regarding EU issues.