The Dark Energy Mystery

Dark energy was first invoked 10 years ago in order to understand the Hubble diagram of distant SN Ia supernovae. Since then, it has emerged as the main component of the Universe. Together with dark matter, it comprises 95% of the Universe; both types having no compelling explanation yet! I will review the main observational evidence in favour of dark energy. I will also present some of the theoretical ideas which could lead to a better understanding of the elusive dark energy of the Universe.