The EU grassland butterfly index integrates the population trends of 17 butterfly species monitored across the EU and is calculated from data from all 27 EU Member States. The start year of national time series ranges from 1990 until 2023, therefore the index is currently also presented as an EU aggregate with smoothed values interpolating annual index values. The data are integrated and provided by the Butterfly Conservation Europe, European Butterfly Monitoring Scheme partnership, and the “Expanding Monitoring of Butterflies for Restoration And Conservation across Europe 2021-2026” (EMBRACE) project.