The use of citizen science offers various benefits to alien species (AS) decision making and to society. Public participation in research and management boosts public engagement and scientific literacy and can reduce conflict in invasive alien species (IAS) management. We report the results of a survey on AS citizen science initiatives within the framework of European Cooperation in Science and Technology (COST) Action Alien-CSI. We gathered metadata on 121 initiatives, excluding general biodiversity reporting portals, across 41 countries spanning from 2005 to 2020 offering the most comprehensive account of initiatives on the continent to date. We retrieved information on project scope, policy relevance, engagement methods, data capture, quality and management, methods and technology applied and performance indicators such as the number of records, participants and publications, etc. The number of projects shows a steep increase in the last 15 years. The highest number of projects run in the UK, Italy, Portugal, France, Spain, Cyprus, Belgium and Croatia. The majority (82%) are focused on biodiversity, 8% on plant health and 5% on human health. Projects are mostly of a contributory nature, spanning a wide array of taxa and environments, and gathering data on occurrences and abundance of AS used for early detection or management. Almost all have data validation procedures in place. About 75% of projects have a focus on the IAS of Union Concern. Despite this policy relevance only half are funded, with government and Life programmes as the most important funding sources. Strikingly, only 30% of the projects indicated that data are shared openly to GBIF or EASIN. Based on this dataset, we hope to offer guidelines to future initiatives in support of project managers, to strengthen the network of IAS citizen science projects and to foster knowledge exchange among citizens, scientists, managers, policy-makers, local authorities, and other stakeholders.