Context Invasive alien species are an important driver of biodiversity loss. Policy responses are developed to address this threat and need to be based on the best available data, including information from alien species registries and occurrence data. The Tracking Invasive Alien Species ( TrIAS ) project implemented a workflow based on FAIR principles to identify new species in Belgium. These are species that have been newly observed on the territory or that were newly added to a species registry or checklist. The workflow is built on the Global Biodiversity Information Facility (GBIF) and uses the Belgian Global Register of Introduced and Invasive Species ( GRIIS Belgium ) as a baseline for comparison. Description This dataset contains the outputs of the pipeline that generates a list of new alien species occurring in Belgium. This pipeline retrieves alien taxa from openly published species checklists or occurrence datasets on GBIF and compares this list with the Global Register of Introduced and Invasive Species - Belgium (GRIIS Belgium) which is published by the IUCN Invasive Species Specialist Group (ISSG). This register is based on the unified checklist of alien species in Belgium which was created by TrIAS in support of research and policy using an open and reproducible workflow. Appearing/reappearing species are defined as follows: Appearing: an alien species which newly occurs on the Belgian territory in the three years before the year of the GBIF download used for creating the occurrence cube for non-native taxa in Belgium . We will refer to this 3 years period as evaluation period . Re-appearing: an alien species reappearing on the Belgian territory after a latency of 4 years or more. For example, we consider a taxon reappearing in 2022 if observations occur in 2022 and 2018 or before. Files appearing_taxa.tsv reappearing_taxa.tsv Field values Field values of <code>appearing_taxa.csv</code>: <code>taxonKey</code>: GBIF taxonKey <code>canonicalName</code>: scientific ...