MecaNano, which stands for "European Network for the Mechanics of Matter at the Nano-Scale", is a European Cooperation in Science & Technology (COST) Action running 2022-2026. The Action is intended as a broad international cooperation aiming to advance the multiscale understanding of the mechanical behavior of nanostructured materials. By combining the expertise of its participants – from experimentalists to simulation, data management and machine learning experts – it aims to overcome the different bottlenecks limiting the exploration of mechanical size effects. MecaNano provides its members with numerous opportunities to interact and collaborate, e.g. through dedicated workshops, symposia and summer schools, or by funding the mobility between participants.