An extended number of people still risk their life today, while illegally crossing the Mediterranean and/or the Aegean Sea as part of an effort to reach a European country. Border management constitutes a crucial tool for effectively dealing with illegal and irregular migration via sea. However, migration and border management literature is lacking studies that address the genuine drivers of migrant crisisfrom a (geo)strategic viewpoint, or rely on the theoretical underpinning of border management from that same angle. This article aims to examine the root causes of a specific national security challenge currently faced by Greece and the EU in large part, namely mixed migratory flows in the Aegean Sea. It explores the theoretical(geo)strategic underpinning of border management at the external EU borders inthe Aegean Sea; merely desk research was used for the collection/analysis of the data. Relevant results suggest that (geo)strategic considerations provide improved understanding not only of the root causes of seaborne migration that are identified as heightened status of insecurity and extreme poverty in the States of origin, but also of strategy formulation in the field of border management at European and national level (Greek sea borders). Results are discussed in terms of existent (geo)strategic theories and models, with a special focus on the ‘strategic thinking in 3D’ framework, the ‘Heartland’ and ‘Rimland’ theses, as well as topographical features and demographics.The aim is to shed light on strategic thinking and planning in the wider domain of security and provide recommendations to improve the current situation.