Highlights from the science case for a 50-100m extremely large telescope

We present an overview of the science case for a 50-100m Extremely Large Telescope. This was the subject of a meeting in Marseilles, France in November 2003, attended by about 50 European astronomers. Four key scientific themes were identified by the participants: terrestrial planets in extra-solar systems; stellar populations across the Universe; building galaxies since the darkest ages; the first objects and re-ionisation structure of the Universe. Although by no means an exhaustive list of science areas in which ELT will have a great impact, these cases provide examples where an ELT can make a dramatic advance in our understanding of the Universe around us. This paper describes these highlighted science themes and the challenging demands they place on ELT performance. See http://www-astro.physics.ox.ac.uk/~imh/ELT/ for more information, including the full list of participants in this work