This chapter examines the profound impact of demographic trends on long-term economic and investment landscapes. It analyzes how slow-moving but irreversible population shifts—such as aging, decline, or growth—affect labor supply, consumption, productivity, savings, and overall economic potential. Through case studies of China, India, the United States, Europe, and Africa, the chapter highlights the economic implications of different demographic structures, including the challenges of low birth rates, population aging, and the opportunities presented by youthful populations. It specifically explores the severe demographic challenges facing East Asia, where fertility rates have fallen far below replacement levels, and contrasts this with the continued growth in regions like Africa. The chapter concludes that understanding these demographic forces is essential for investors to identify long-term risks and opportunities, adapt strategies to future global growth patterns, and navigate a world characterized by slowing population growth and increasing longevity.