Population ageing has become an increasing challenge of our time. The process of demographic ageing is more intense in the Balkan countries, some of which have already held the world’s top positions. This paper examines the trends of population ageing in the Balkans and the South East Europe (SEE) countries (Albania, Bosnia and Herzegovina, Bulgaria, Greece, FYR of Macedonia, Romania, Slovenia, Serbia, Montenegro, and Croatia) at the beginning of the 21st century and the cross-country differences in the timing of the ageing process. In addition to the analysis of an overall effect of the main factors, this paper examines the influence of population ageing on labour force in the Balkan countries. There are three factors behind the increases in the share of the population aged 65 and over: declining fertility rates in recent decades which have reduced the relative number of young people, the rise in life expectancy and the cohort of baby boomers over the age of 60. The ageing of the Balkan countries population introduces several major policy challenges. Paper highlights the impact of population ageing on human resources and labor supply. [Projekat Ministarstva nauke Republike Srbije, br. 047006]