The fertility transition in Thailand has been one of the most rapid among Asian countries that are yet to attain newly industrialized country status. In the early 1960s, the total fertility rate exceeded six births per woman; currently, it stands at 1.9 or slightly below replacement level. At present, it is hard to predict the future trend in fertility as this involves several factors that need much closer study, in particular, fertility preferences, changes in marriage patterns and the wider effects of the current economic crisis in Thailand. Rapid declines in fertility and mortality have had a profound effect on the age structure of the population, notably the increasing elderly proportion. Thailand now faces new challenges and priorities for population policy. Policy responses to concerns arising from below-replacement fertility will be much more complex and involve greater government activism, improved institutional capacities and more resources than in the past. This paper reviews the fertility transition in Thailand and looks at some consequences and policy implications of low fertility, with special reference to the family and the elderly population.