Citizen science, the active involvement of non-professional scientists in research, comes in great variety, from small group projects based on common interest, to large, international projects with professional scientists and research institutions. Many scientists at LERU universities enthusiastically engage with citizen science in many domains. Citizen science can contribute to the quantity and quality of research and can benefit researchers and society at large. To do so, citizen science must adhere to what are considered fundamental research principles, methods and procedures to ensure quality and validity. The paper analyses trends in citizen science, formulates guidelines for scientists, and formulates recommendations for universities, research funding organisations and policy makers, from raising awareness to developing ways of assessing and recognising citizen science in research funding and evaluation processes.