This paper analyses economic implications of the different ways in which the population structure of countries becomes older: longer lives and declines in fertility both generate ageing populations but have very different impacts upon the aggregate population. If lower fertility persists populations in many countries will decline. Having reviewed the evidence for this, I consider both why fertility rates have fallen and may stay low. I then analyse the economic implications of populations that may stop growing and start to fall, focusing on how this may play out in the UK. I consider policy implications of such a demographic shift. Despite many predictions of the dire consequences of falling populations the economic impacts are likely, on balance, to be positive.

本文分析了各国人口结构老龄化的不同方式的经济影响：寿命延长和生育率下降都会导致人口老龄化，但对总人口的影响却截然不同。如果低生育率持续存在，许多国家的人口将会减少。在回顾了这方面的证据之后，我考虑了为什么生育率已经下降并可能保持在低水平。然后，我分析了可能停止增长并开始下降的人口的经济影响，重点关注这在英国可能产生的影响。我考虑了这种人口变化的政策影响。尽管对人口下降的可怕后果有许多预测，但总的来说，经济影响可能是积极的。