Around fifteen thousand fieldworkers annually count breeding birds using standardized protocols in 30 European countries. The observations are collected by using country-specific and standardized protocols, validated, summarized and finally used for the production of continent-wide annual and long-term indices of population size changes of 170 species. Here, we present the database and provide a detailed summary of the methodology used for fieldwork and calculation of the relative population size change estimates. We also provide a brief overview of how the data are used in research, conservation and policy. We believe this unique database, based on decades of bird monitoring alongside the comprehensive summary of its methodology, will facilitate and encourage further use of the Pan-European Common Bird Monitoring Scheme results. The Pan-European Common Bird Monitoring Scheme database is organised into five datasets: (1) European species indices, (2) European species trends, (3) European species trends for three short periods, (4) a list of details on the national monitoring schemes and (5) a matrix of countries providing data for population size estimates of individual species. Moreover, national-level species indices and uncertainty estimates are also available in the PECBMS database. Due to specific privacy ownership rights, the most recent (2016-2017) data from Spain (10.5281/zenodo.4590140) and Cyprus (10.5281/zenodo.4590189) are under Restricted Access and researchers interested in these most recent updates are required to provide a brief description of the data use. The Austrian and Portuguese datasets are publicly available but researchers using these datasets are kindly requested to notify the national scheme coordinators of their use. A list of regularly updated contacts to all national scheme coordinators is provided at the PECBMS website (https://pecbms.info/country/). We aim to maintain the PECBMS database with annual updates. The annual updates will be available through the PECBMS database deposited at this Zenodo repository to ensure long-term public availability of the data. Updates on data acquisiton and data processing in the dataset released in 2021 are available from: https://pecbms.info/what-is-new-in-2021-data-update/ Updates on data acquisiton and data processing in the dataset released in 2022 are available from: https://pecbms.info/what-is-new-in-2022-data-update/ Updates on data acquisiton and data processing in the dataset released in 2023 are available from: https://pecbms.info/what-is-new-in-2023-data-update/