Waarnemingen.be / observations.be - List of species observed in Belgium is a species checklist dataset published by Natuurpunt and Natagora. Waarnemingen.be (in Dutch) and observation.be (in French) are the two local Belgian subsites of the global observation.org website. The checklist comprises 18.785 species observed in Belgium. Here, it 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), its status (native, introduced) and first and last observation date per region (Flanders, Brussels Capital Region, Wallonia) in Belgium (in the distribution extension). Only observations which were approved by species specialists based on provided evidence (photograph or sound), or which were approved based on expert judgment by the validating experts were considered for publication (see Swinnen et al. 2022 for the validation procedure). Observers’ data-sharing settings were respected at all times. When the first or last observation from a species in a region was not to be shared, observers were contacted to request an exception for this species list. In the few cases this authorisation was not acquired, the next (for the oldest record) or previous (for the most recent record) observation date was considered for publication. This species list does not represent a complete overview of Belgian biodiversity, only species that are recorded in the citizen science platforms waarnemingen.be and observation.be. Other datasets and checklists have to be considered for the compilation of a complete Belgian overview. We have released this dataset under a Creative Commons Attribution 4.0 International License (CC-BY 4.0). We would appreciate it, however, if you read and follow these norms for data use (http://www.natuurpunt.be/normen-voor-datagebruik). If you use these data for a scientific paper, please cite the dataset following the applicable citation norms and/or consider us for co-authorship. We are always prepared to provide more information or knowledge on how to use the data, so please contact us via the contact information provided in the metadata or natuurdata@natuurpunt.be. This dataset was published as open data for the TrIAS project (Tracking Invasive Alien Species http://trias-project.be, Vanderhoeven et al. 2017, Groom et al. 2022), with technical support provided by the Research Institute for Nature and Forest (INBO). The subset of introduced species is selected as one of the authoritative sources for the compilation of a unified and reproducible checklist of alien species in Belgium published as the Global Register of Introduced and Invasive Species - Belgium (Desmet et al. 2021). This way, validated newly reported alien species on the waarnemingen.be/observation.be citizen science portal (Swinnen et al. 2018) quickly find their way to the scientific tools supporting alien species policies and management in Belgium.