This paper serves as a starting point for the ENGAGE project, and in particular, its final output: the White Paper on Joined-up, Coherent, Sustainable and Effective EU External Action.The paper lays common ground for the project in two ways. First, drawing on primary documents and literature, the paper puts forward shared definitions of the effectiveness, coherence and sustainability of the EU’s external action. Over the next three years, the ENGAGE consortium will engage in research on various aspects of the EU’s external action following the definitions presented in this paper. Furthermore, the publication also reflects on how indicators can be developed to assess whether various areas of the EU’s external action achieve the objectives of effectiveness, coherence and sustainability. Second, this study lays the foundation for the final product of the ENGAGE project – the White Paper, which will be published in 2024, providing recommendations on how to accommodate multiple action domains for effective, coherent and sustainable external action. The ENGAGE project understands a White Paper as: an actionable programme for the EU, addressing specific problems and solutions in a particular policy area and supplying detailed policy recommendations to operationalise proposed solutions. The present paper also discusses the scope and content of the planned strategic document, as well as its specific objectives and the features that distinguish it from similar publications by other think thank experts and academics. In particular, this study reflects on the envisaged validation process of the White Paper, which will precede its dissemination, and aim to gather insights and feedback from a wide range of stakeholders on the proposed policy recommendations.