<p>This paper examines recent demographic dynamics in Spain, France, and Italy by analysing regional patterns of population turnover and the relative role of natural and migratory components. Building on the fast-slow demography framework, the study employs the Population Turnover Rate (PTR), the Migration Share of Turnover (MST), and the Birth Share of Turnover (BST) to assess how demographic change unfolded across NUTS-2 regions between 2014 and 2023. Although the three countries share geographical proximity and face comparable structural challenges, their demographic trajectories appear to diverge in various ways, partly reflecting differences in fertility levels, ageing patterns, and migration regimes. Special attention is devoted to Mediterranean coastal regions, where migration-driven demographic change has accelerated in recent years. The results suggest the possible formation of a demographic corridor along the Mediterranean rim, especially between the Spanish and French coasts, where relatively high turnover and a growing role of mobility-related processes seem to be taking shape. Yet this transnational coastal dynamism is not uniform. National contexts continue to structure regional outcomes, shaping the balance between mobility-driven (fast) and natural (slow) demographic processes. In Spain and France, coastal regions exhibit clear demographic distinctiveness linked to strong residential attractiveness, especially among older adults. In Italy, by contrast, geographical differences are less pronounced, as most regions benefit from similar coastal or amenity environments. The paper concludes by discussing how ageing, environmental pressures, and evolving residential mobility may shape the future demographic trajectories of these coastal areas.</p>