This document discusses citizen science projects focused on biodiversity in Europe. It provides background on citizen science, describing it as scientific research conducted in whole or in part by amateur or nonprofessional scientists. It then highlights several examples of biodiversity monitoring projects in Europe, including waarnemingen.be, waarneming.nl, observado.org, artportalen.se, and naturgucker.de. These projects engage citizens to record and report observations of taxa in nature. The document compares the scale of these projects in terms of numbers of observations, users, and other collected data.