An ever greater number of our contemporaries will reach a very much greater age than their ancestors. Longevity is one of the most fertile fields for paradoxes: it is clear that the same causes do not produce the same effects at the age of ten and at the age of one hundred! On the subject of longevity, the "recipe book" is far from having been written. Nevertheless, the Fondation IPSEN has chosen a few of these paradoxes to discuss and try and explain them.