I will discuss recent advances in applying Lagrangian dynamics in understanding the gravitational clustering of dark matter on the mildly-nonlinear scales. Perturbative results will be presented up to the one-loop order. I will show how the formalism can be extended to describe the statistics of generic biased tracers (e.g. galaxies) and to include the redshift space effects. Applications to the baryon acoustic oscillations and CMB lensing will also be discussed.