Looking at the dark side: weak lensing by large scale structure

Intervening structures in the universe give rise to small distortions
in the shapes of distant galaxies. By measuring this tiny coherent
signal, we can study the mass distribution in the universe directly,
without relying on baryonic tracers. This makes weak lensing by
large-scale structures a powerful probe of cosmology. It allows us to
differentiate between dark energy models or modifications of the law
of gravity. I will briefly review the topic of cosmic shear and
discuss how the signal is extracted from the data and present results
from the recently completed analysis of the CFHT Legacy Survey.