The impressive surge of perovskite solar cells has been accompanied by a comparable effort to unveil the basics properties of this class of materials. Theoretical and computational modeling is playing a major role in providing scientists an in depth atomistic view of the intimate perovskite properties contributing to the success of this class of materials. In this chapter we discuss recent advances in our understanding of organohalide perovskites based on first principles calculations and molecular dynamics simulations. Emphasis is placed on the interplay of electronic and structural features and on the important role of the organic cation and of its dynamics in dictating the peculiar material’s properties. The role of chlorine doping in methylammonium lead iodide and of interfaces with TiO2 in solar cells models are finally described.