The world's population reached the 6 billion mark in 1999. By the middle of this new century, it may well number 9 billion. Why is this increase occurring? Will it come to a halt? What are the mechanisms that control population trends? What issues are being raised by population growth? Can we really talk about global population as such, or is it more a matter of different populations following their own demographic rhythms, under a wide variety of economic and social conditions? By touching on these different questions, this publication endeavours to decode the human adventure as it is "measured" by demography.