Rapid population ageing and the influx of baby boomers arriving at the age of retirement is generating a considerable threat for the financial sustainability of Belgium’s old-age pension system. Concurrently to a trend observed in many developed countries, Belgium has witnessed an upward trend in male employment rates starting in the 2000’s and a long-term structural increase in female employment. While these tendencies in employment show potential for improving the financial sustainability of the pension system, they are in no way sufficient to absorb the overwhelming burden of population ageing on public old age spending. Confronted with these demographic trends, the Belgian government has implemented various social security reforms since the 1990’s to safeguard the financial sustainability of the pension system. The objective of the thesis is to explore the impact of the social security system as a driver of retirement, using Belgium as a case study.