The Large Synoptic Survey Telescope (LSST) is an automated ground-based 8.4m optical telescope, whose first observations are expected in 2023. The aim of this new instrument is to conduct a ten year wide and deep imaging survey of 18,000 square degrees of the sky in six broad optical bands, with a deep stack reaching magnitude $r=27.5$. The LSST design is driven by four science themes: dark energy and dark matter, galactic structure, transient objects, and the Solar System inventory. After a quick presentation of the LSST subsystems and of the project status, I will focus on the LSST cosmological probes, and more specifically on the large-scale structures and weak lensing science reaches. I will highlight the on-going preparation studies about the photometric redshift reconstruction for galaxies and the possibilities in terms of cross-correlations with other cosmological data and surveys.