<p>Alien species represent a global challenge to biodiversity and human society. In many parts of the world, however, they remain poorly documented. Here we review citizen science datasets and published avifaunal inventories to collate and document the scale and scope of alien bird species in Indonesia, an archipelago which, because of the well-documented pet bird trade, may reasonably be expected to have a high incidence of alien birds. We identify and map the non-native Indonesian ranges of 38 avian alien species, a number that has increased nearly three-fold since 1980, driven largely by an increase in the number of alien songbirds. These 38 species have native and non-native ranges that overlap with known trade and pet bird ownership hotspots in Indonesia, and have higher trade prevalence than would be expected by chance. We determine that Indonesia’s alien bird species have probably become established as a direct consequence of the bird trade. Likely means of establishment include from trade markets and households, post-confiscation releases by government authorities, merit releases and mercy releases. The consequences of so many avian alien species are unknown but unlikely to be positive; this represents an obvious avenue for future research.</p>