Radiation measurements by citizen appeared for the first time in the aftermath of the Chornobyl accident and received a renewed interest in the aftermath of the Fukushima accident. At that time, several networks of citizen measurement of radioactivity appeared in Europe, mainly acting for education to radioactivity and the science of measurement and for education, both initial and continuous, to risks associated to radioactivity. However, these networks suffer from a lack of sustainability due to several parameters, including lack of long-term funding, lack of credibility of citizen-led data and lack of applications in data use. This review identifies and details challenges that these networks have to face with, and opportunities they can use to increase the useability of citizen measurement data.