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. I will review the topic of cosmic shear and discuss how the signal is extracted from the data. I will present results from recent surveys, most notably the CFHT Legacy Survey and COSMOS and discuss future directions.
