Beginning with a discussion of the sources and quality of Indonesian age data by sex, this paper examines the changes in the functional age groups of the population of Indonesia from 1971 to the year 2005, and the implications of these changes for education, labour force participation, dependency ratios and fertility. Data for the period 1971 to 1985 are based on actual enumerations, while those for the period 1990 to 2005 are based on projections. Although he provisional totals of the 1990 Census had been released before the publication of this paper. their breakdown by age was still not available. The functional age categories discussed in the paper include the pre-school years, the primary and intermediate school ages, the teenage years, the reproductive ages of women, the principal working ages and the post-work years. It concludes with a discussion of various policy and planning implications of these changes.