n Citizen Science, members of the general public collaborate with scientists to generate and use data relating to the natural world. For the many fields of marine research, this is a particularly powerful approach which should not be overlooked. The sheer scale of coastal and ocean environments mean that it would take several lifetimes for scientists to study them alone. By collaborating with citizens, a much greater number of people can be mobilized to gather a wealth of data and develop new scientific knowledge and understanding. The variety of data types which are amenable to Citizen Science, as outlined in the position paper, are great, meaning that there could be a project to suit everyone. Citizen Science can also enable participants to improve their Ocean Literacy, gain new skills and experiences, and can also empower them to participate in the process of delivering future marine policy.Now, more than ever, marine science research is needed to understand the impacts of a world undergoing change. The rise of Marine Citizen Science to help address this need is therefore timely. This paper highlights opportunities, challenges and best practice in Marine Citizen Science, and sets out a list of high-level strategic recommendations for the future development of Marine Citizen Science in Europe. It presents examples of existing Marine Citizen Science initiatives in Europe to illustrate good practice. Common concerns such as data quality and maintaining engagement are discussed, as are future opportunities such as increased use of technology and potential role of Marine Citizen Science in informing marine policy and conservation. The paper closes with a list of high-level strategic recommendations for the future development of Marine Citizen Science in Europe.