With the accession to the European Union, Portugal became part of an area that has been moving towards greater economic and political integration. In this process, Member States have delegated part of their powers to European institutions, hoping that decisions on matters of joint interest can be made more effectively at European level. However, the current economic and financial crisis has revealed weaknesses in the European construction process that have highlighted the difficulties in achieving the convergence of Member States’ national interests. In these circumstances, this study aims to evaluate whether Portugal’s interest is being properly safeguarded given the strategies and common policies enacted by the European Union within the framework of security and defence policies and affairs of the sea. To this end, the concept of national interest is analysed in the first part in order to establish a common understanding of the subject. In the second part, Portugal’s current interests are identified and the third examines EU’s interests in the areas under review. The fourth part reflects on how national interests connect with European interests, seeking to highlight the opportunities to be seized and the threats to be addressed. The analysis concluded that it is not easy to identify a clear European interest in the field of security and defence, while in the area of maritime affairs that interest is evident and requires securing the exclusive competence of the Union in the management of the biological resources of the sea. The defence of Portugal’s national interest requires proper monitoring of the negotiations leading to the building of sector strategies and common EU policies.