The publication of this IDN Cadernos, dedicated to the III Seminar of the Atlantic Centre, aims to make public the contributions collected during this event that gathered on October 19, 2021, in Lisbon, a group of experts on Atlantic issues. The objective was to reflect on existing multilateral and multinational initiatives, helping to identify dynamics and formats of cooperation and complementarity that contribute to generating lasting solutions to common security threats in the shared regional context of the Atlantic.