This dissertation provides a comprehensive analysis of the relationship between global demographic trends and international capital flows. The first chapter employs an overlapping generations model to dissect how factors like fertility rates and longevity impact capital flows leading to cross-country fiscal spillovers. The second chapter uses panel data from 46 advanced and emerging economies to validate these theoretical findings, confirming that early aging in advanced countries has been advantageous for emerging economies. The third chapter extends the focus to real interest rates, revealing that they are shaped by both local and global demographic structures. The degree of a country's financial integration also influences its interest rates' sensitivity to global demographic trends. By illuminating these complex interactions, this dissertation significantly advances our understanding of global capital flows. It also provides invaluable insights for policymakers navigating the financial implications of demographic changes in an interconnected world economy.