The large-scale structure of the universe is becoming the leading probe of cosmology. The ongoing and future LSS surveys combined with the next generation CMB experiments aim to provide the unprecedented constraints on the statistic of the initial conditions and physics of inflation, to measure the sum of neutrino masses and to shed new light on the nature of dark matter and dark energy. The main theoretical challenge in this program is understanding the nonlinear evolution of density fluctuations induced by gravitational collapse. In this talk I will describe several analytical tools to deal with this problem. In the first part I will focus on some nonperturbative results such as consistency relations for LSS and their applications to the modeling of the nonlinear evolution of the BAO peak. In the second part I will describe perturbation theory approach to gravitational nonlinearities, its advantages, successes and limitations. As a final remark I will present some recent progress in evaluation of higher order/loop correlation functions using scattering amplitudes of a massless QFT.