Indonesia's Constitutional Court is considered as one of Asia's most activist courts. In this paper we investigate empirically the determinants of judicial behaviour at the Constitutional Court of Indonesia in the period 2003-2017. The paper draws on a unique data set of 80 high profile political cases complemented by data on the socio-biographic profiles of judges on the bench. We start off by describing patterns in judicial decision making across time and court benches, before seeking to test more specifically for the impact of the judges' professional background, presidential terms, Chief Justice influence and appointment tracks. We discuss these empirical results in the context of Indonesia's evolving constitutional democracy and the implications for the comparative judicial politics literature on judicial behaviour.