This chapter outlines the nature and causes of demographic (population) aging. Diversity is a global feature, with countries and regions worldwide at rather different stages in terms of percentages of older persons. Falling and sometimes very low fertility has generally caused the demographic aging of populations, although greater life expectancy also plays a part. The chapter outlines effective age of retirement and labor force participation of older workers and the key aspects of the 2002 Madrid International Plan of Action on Ageing. Selected issues arising from aging workforces are examined: older workers' skills; unemployment and underemployment; mental and physical changes; and age bias and workplace discrimination. The future implications of the interplay between population aging on economic growth are introduced.