The Performance Review Body (PRB) has published the 2023 Annual Monitoring Report and Traffic Light System - part of its yearly review of how Single European Sky (SES) Member States are performing. In 2023, air traffic in the SES Member States rose to 91% of pre-pandemic levels, yet the capacity performance of air traffic management continued to deteriorate. Although financial resources were available, investment in staff and capacity projects by certain air navigation service providers was insufficient, which meant that the traffic surge following the pandemic could not be fully accommodated. This does not only affect the Member States concerned, but the entire network. (....)