The Checklist of alien birds of Belgium is a species checklist dataset published by the Research Institute for Nature and Forest (INBO). It contains information on 244 alien birds species occurring or ever observed in the wild in Belgium since 1800 and is is a compilation of different sources: literature (e.g. scientific papers, reports), citizen science portals (e.g. observations.be, waarnemingen.be, the Belgian Rare Birds Committee http://www.belgianrbc.be) and online databases such as DAISIE (DAISIE 2000) or the Global Avian Invasions Atlas (Dyer et al. 2017). Here, the checklist is published as a standardized Darwin Core Archive and includes for each species: the scientific name, higher classification and stable taxon identifier (in the taxon core), the presence in Flanders, Wallonia and the Brussels-Capital Region, as well as the year of the first introduction (first collection) and/or last assessment/observation in Belgium (given as a year range in the event date in the distribution extension), coarse habitat information (in the species profile extension), and the pathway(s) of introduction, native range(s) and degree of establishment in Belgium (in the description extension). The checklist can be used for research, to inform horizon-scanning exercises, to perform risk assessments of alien species, to compile regional and national registries of alien species, to feed biodiversity indicators etc. Issues with the dataset can be reported at https://github.com/trias-project/alien-birds-checklist We have released this dataset to the public domain under a Creative Commons Zero waiver. We would appreciate it if you follow the GBIF citation guidelines (https://www.gbif.org/citation-guidelines) when using the data. If you have any questions regarding this dataset, don’t hesitate to contact us via the contact information provided in the metadata or via opendata@inbo.be. This dataset was published as open data for the TrIAS project (Tracking Invasive Alien Species http://trias-project.be, Vanderhoeven et al. 2017), with technical support provided by the Research Institute for Nature and Forest (INBO). It is selected as one of the authoritative sources for the compilation of a unified and reproducible checklist of alien species in Belgium (Desmet et al. https://doi.org/10.15468/xoidmd). The compilation of the checklist was supported by the Short Term Scientific Mission Improving data flows for alien birds in Belgium and drafting a roadmap for alien species citizen science in Romania funded by the European Cooperation in Science and Technology (COST) Alien CSI CA17122 - Increasing understanding of alien species through citizen science (https://alien-csi.eu/).