I will review recent progresses we made understanding theoretically the large scale structure in the universe using computer simulations. I will first discuss the N body approach, trying to assess the level of accuracy one can reach using modern N body codes. I will then briefly discuss recent effort to go beyond the N body approach, and/or to go beyond general relativity as there basic framework. I will then focus on the main source of uncertainty, namely baryonic physics. Although we believe the effect of baryonic physics are likely to be strong enough so that we have to worry about them, I will discuss a methodology we could use to minimise their effect in the cosmological parameter estimation.
