Population aging is one of the most profound demographic transformations of the twenty-first century, driven by declining fertility and increasing life expectancy. While historically associated with high-income nations, this demographic transition is now unfolding rapidly across the Global South, including India. Aging is not merely a biological process but a complex socio-demographic phenomenon shaped by improvements in healthcare, education, nutrition, and living standards. Its implications are far-reaching, impacting economic productivity, healthcare systems, pension frameworks, and patterns of intergenerational support. This chapter introduces the Demography of Aging part, which brings together diverse contributions that examine the multifaceted dimensions of aging across varied cultural, economic, and policy contexts. Through empirical evidence and theoretical insights, the chapters explore demographic transitions, social and economic consequences, and policy responses to aging populations. Together, these contributions emphasize the diverse nature of aging across contexts and stress the critical need for inclusive and contextually appropriate strategies to safeguard the well-being and dignity of older adults around the world.