Fertility in all but 12 countries in the world is now falling. Where will it stop? In this talk, Prof David Coleman looks at the demographic transition in the developing world. Conventionally the demographic transition was expected to end when birth rates reached replacement level. That has not happened. Birth rates in the developed world are mostly below it, some markedly so. What will happen in the developing world? Some populations have been very slow to begin the fertility decline, a handful have not even started. Their populations will become disproportionately large. In others (Pakistan, Kenya) decline has stalled - we do not yet know whether permanently or not. But in many developing Asian countries, and some on Latin America, birth rates have already fallen below replacement. As many such countries have a 'familist' family structure (as in Spain, Italy, Greece) birth rates my reach very low levels - raising the prospect that (outside Africa) NW European countries might have the highest birth rate in the world by mid-century, in a future of demographic diversity and uncertainty. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/