Part I. Comets and their origin. Introduction

The formation of comets

Astrochemistry : water and organic molecules in comets

The asymmetry of life

Part II. The Rosetta Mission : rendezvous with a comet. The Rosetta Cometary Mission : launch and target comet

On the way to Comet 67P/Churyumov-Gerasimenko

Rosetta's rendezvous with the comet

Conclusions and outlook.