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The United Nations Population Division has just pu-blished the final version of a bold exercise in popu-lation projection: several scenarios of the future of every country in the world to 2300 [1]. According to the study, the world population will continue to grow ra-pidly until 2075, reaching a historic high of 9.2 billion, compared with 6.4 billion now, and then gradually sta-bilize at around 9 billion. But this is only the central sce-nario, based on the assumption that the fertility rate will eventually settle at the replacement level, i.e. 2.1 children per woman. The United Nations demogra-phers also show that by adding or subtracting a few de-cimal points to this rate (plus or minus 0.5 children per woman on average until 2050, then 0.25 thereafter), the world population would rise to 36.4 billion or fall to 2.3 billion in three centuries ’ time. Given this extraordinarily broad range, it is easy to be sceptical about the value of the exercise. Researchers who prefer probabilistic projections, i.e. with clearly defined confidence intervals, are unimpressed [2, 3]. Finding out that there is a 95 % chance of the world pop-ulation being somewhere between 2 billion and 36 bil-lion in 2300 does not tell us much. But, anticipating that criticism, the UN’s demographers assert that the pro-jections are not intended to be forecasts of the future, but extrapolations of current trends with a target. They The world population over the next three centuries: explosion, implosion or equilibrium? François Héran*