The chapter explores how partisanship affects political engagement and support, paying specific attention to new parties. Using panel data collected in Spain during a period of profound party system change, the authors estimate the extent to which partisanship with new parties influences citizens’ levels of interest in politics and trust in political institutions. Developing an identification with a new party increases levels of political interest, but only for individuals without a prior party identification. This effect is not very different to the one produced by acquiring an identification with an old party: new parties seem to work much like old parties do. On the other hand, partisanship with new parties does not increase levels of trust in political institutions. The chapter discusses these findings and elaborates on the methodological challenges of analysing the consequences of partisan change along time.