The recently adopted Electricity Market Design (EMD) reform includes provisions for the creation of Flexibility Needs Assessments (FNAs) on the national and European level. The reform sets a focus on advancing decarbonization while maintaining a high level of supply security. The FNAs should further enable Member States to set up mechanisms to procure additional flexibility to meet any identified inefficiencies due to an insufficiently inflexible the system. Against this background, the JRC reviewed existing flexibility assessments in the literature based on what outcomes they produce. Based on this review, we propose that FNAs in Europe should assess three key areas: renewable integration, ramping needs and reserve requirements. We further propose concrete indicators, which allow to derive net flexibility needs – taking into consideration the capabilities already present in the system – and enable Member States to procure any missing volumes of flexibility.