This Reprint examines the complex interplay between demographic trends and regional economic development. Persistent regional inequalities, population decline, low fertility, and aging populations pose significant challenges to social cohesion, economic sustainability, and long-term development. Using contemporary demographic analysis and regional science methods, this research highlights the structural and socio-economic drivers of demographic change and explores their implications for policy design. Case studies span Greece, Italy, the United States, Thailand, and the Middle East, providing insights into global patterns of demographic and regional disparities.